From 372b4e191c9fc2566dac88bd2f543fc931a1c601 Mon Sep 17 00:00:00 2001
From: Abhimanyu Saharan <asaharan@onemindservices.com>
Date: Fri, 13 Feb 2026 22:01:18 +0530
Subject: [PATCH] feat: implement custom field form and utility functions for
 managing custom fields

---
 .../[boardId]/TaskCustomFieldsEditor.test.tsx |  84 +++
 .../[boardId]/TaskCustomFieldsEditor.tsx      | 155 +++++
 .../[boardId]/custom-field-utils.test.tsx     | 150 +++++
 .../boards/[boardId]/custom-field-utils.tsx   | 329 ++++++++++
 frontend/src/app/boards/[boardId]/page.tsx    | 608 +-----------------
 .../app/custom-fields/[fieldId]/edit/page.tsx | 548 +---------------
 frontend/src/app/custom-fields/new/page.tsx   | 482 +-------------
 frontend/src/app/custom-fields/page.tsx       |   9 +-
 .../custom-fields/CustomFieldForm.test.tsx    | 136 ++++
 .../custom-fields/CustomFieldForm.tsx         | 368 +++++++++++
 .../custom-fields/CustomFieldsTable.tsx       |  13 +-
 .../custom-fields/custom-field-form-types.ts  |  63 ++
 .../custom-field-form-utils.test.ts           | 167 +++++
 .../custom-fields/custom-field-form-utils.ts  | 273 ++++++++
 14 files changed, 1808 insertions(+), 1577 deletions(-)
 create mode 100644 frontend/src/app/boards/[boardId]/TaskCustomFieldsEditor.test.tsx
 create mode 100644 frontend/src/app/boards/[boardId]/TaskCustomFieldsEditor.tsx
 create mode 100644 frontend/src/app/boards/[boardId]/custom-field-utils.test.tsx
 create mode 100644 frontend/src/app/boards/[boardId]/custom-field-utils.tsx
 create mode 100644 frontend/src/components/custom-fields/CustomFieldForm.test.tsx
 create mode 100644 frontend/src/components/custom-fields/CustomFieldForm.tsx
 create mode 100644 frontend/src/components/custom-fields/custom-field-form-types.ts
 create mode 100644 frontend/src/components/custom-fields/custom-field-form-utils.test.ts
 create mode 100644 frontend/src/components/custom-fields/custom-field-form-utils.ts

diff --git a/frontend/src/app/boards/[boardId]/TaskCustomFieldsEditor.test.tsx b/frontend/src/app/boards/[boardId]/TaskCustomFieldsEditor.test.tsx
new file mode 100644
index 00000000..a0dcab03
--- /dev/null
+++ b/frontend/src/app/boards/[boardId]/TaskCustomFieldsEditor.test.tsx
@@ -0,0 +1,84 @@
+import { fireEvent, render, screen } from "@testing-library/react";
+import { describe, expect, it, vi } from "vitest";
+
+import type { TaskCustomFieldDefinitionRead } from "@/api/generated/model";
+import { TaskCustomFieldsEditor } from "./TaskCustomFieldsEditor";
+
+const buildDefinition = (
+  overrides: Partial<TaskCustomFieldDefinitionRead> = {},
+): TaskCustomFieldDefinitionRead => ({
+  id: "field-1",
+  organization_id: "org-1",
+  field_key: "client_name",
+  field_type: "text",
+  ui_visibility: "always",
+  label: "Client name",
+  required: false,
+  default_value: null,
+  description: null,
+  validation_regex: null,
+  board_ids: ["board-1"],
+  created_at: "2026-01-01T00:00:00Z",
+  updated_at: "2026-01-01T00:00:00Z",
+  ...overrides,
+});
+
+describe("TaskCustomFieldsEditor", () => {
+  it("renders loading and empty states", () => {
+    const { rerender } = render(
+      <TaskCustomFieldsEditor
+        definitions={[]}
+        values={{}}
+        setValues={vi.fn()}
+        isLoading
+        disabled={false}
+      />,
+    );
+
+    expect(screen.getByText("Loading custom fields…")).toBeInTheDocument();
+
+    rerender(
+      <TaskCustomFieldsEditor
+        definitions={[]}
+        values={{}}
+        setValues={vi.fn()}
+        isLoading={false}
+        disabled={false}
+      />,
+    );
+
+    expect(
+      screen.getByText("No custom fields configured for this board."),
+    ).toBeInTheDocument();
+  });
+
+  it("updates field values and respects visibility rules", () => {
+    const setValues = vi.fn();
+    render(
+      <TaskCustomFieldsEditor
+        definitions={[
+          buildDefinition({
+            field_key: "hidden_if_unset",
+            ui_visibility: "if_set",
+          }),
+          buildDefinition({ id: "field-2", field_key: "client_name" }),
+        ]}
+        values={{}}
+        setValues={setValues}
+        isLoading={false}
+        disabled={false}
+      />,
+    );
+
+    expect(screen.queryByText("hidden_if_unset")).not.toBeInTheDocument();
+
+    fireEvent.change(screen.getByRole("textbox"), {
+      target: { value: "Acme Corp" },
+    });
+
+    const updater = setValues.mock.calls.at(-1)?.[0] as (
+      prev: Record<string, unknown>,
+    ) => Record<string, unknown>;
+    expect(updater({})).toEqual({ client_name: "Acme Corp" });
+  });
+});
diff --git a/frontend/src/app/boards/[boardId]/TaskCustomFieldsEditor.tsx b/frontend/src/app/boards/[boardId]/TaskCustomFieldsEditor.tsx
new file mode 100644
index 00000000..c0e31042
--- /dev/null
+++ b/frontend/src/app/boards/[boardId]/TaskCustomFieldsEditor.tsx
@@ -0,0 +1,155 @@
+import type { Dispatch, SetStateAction } from "react";
+
+import type { TaskCustomFieldDefinitionRead } from "@/api/generated/model";
+import { Input } from "@/components/ui/input";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import { Textarea } from "@/components/ui/textarea";
+
+import {
+  customFieldInputText,
+  isCustomFieldVisible,
+  parseCustomFieldInputValue,
+  type TaskCustomFieldValues,
+} from "./custom-field-utils";
+
+type TaskCustomFieldsEditorProps = {
+  definitions: TaskCustomFieldDefinitionRead[];
+  values: TaskCustomFieldValues;
+  setValues: Dispatch<SetStateAction<TaskCustomFieldValues>>;
+  isLoading: boolean;
+  disabled: boolean;
+  loadingMessage?: string;
+  emptyMessage?: string;
+};
+
+export function TaskCustomFieldsEditor({
+  definitions,
+  values,
+  setValues,
+  isLoading,
+  disabled,
+  loadingMessage = "Loading custom fields…",
+  emptyMessage = "No custom fields configured for this board.",
+}: TaskCustomFieldsEditorProps) {
+  if (isLoading)
+    return <p className="text-xs text-slate-500">{loadingMessage}</p>;
+  if (definitions.length === 0) {
+    return <p className="text-xs text-slate-500">{emptyMessage}</p>;
+  }
+
+  return (
+    <div className="space-y-3">
+      {definitions.map((definition) => {
+        const fieldValue = values[definition.field_key];
+        if (!isCustomFieldVisible(definition, fieldValue)) return null;
+
+        return (
+          <div key={definition.id} className="space-y-1">
+            <label className="text-[11px] font-semibold uppercase tracking-wide text-slate-500">
+              {definition.label || definition.field_key}
+              {definition.required === true ? (
+                <span className="ml-1 text-rose-600">*</span>
+              ) : null}
+            </label>
+
+            {definition.field_type === "boolean" ? (
+              <Select
+                value={
+                  fieldValue === true
+                    ? "true"
+                    : fieldValue === false
+                      ? "false"
+                      : "unset"
+                }
+                onValueChange={(value) =>
+                  setValues((prev) => ({
+                    ...prev,
+                    [definition.field_key]:
+                      value === "unset" ? null : value === "true",
+                  }))
+                }
+                disabled={disabled}
+              >
+                <SelectTrigger>
+                  <SelectValue placeholder="Optional" />
+                </SelectTrigger>
+                <SelectContent>
+                  <SelectItem value="unset">Optional</SelectItem>
+                  <SelectItem value="true">True</SelectItem>
+                  <SelectItem value="false">False</SelectItem>
+                </SelectContent>
+              </Select>
+            ) : definition.field_type === "text_long" ||
+              definition.field_type === "json" ? (
+              <Textarea
+                value={customFieldInputText(fieldValue)}
+                onChange={(event) => {
+                  const nextFieldValue = parseCustomFieldInputValue(
+                    definition,
+                    event.target.value,
+                  );
+                  setValues((prev) => ({
+                    ...prev,
+                    [definition.field_key]: nextFieldValue,
+                  }));
+                }}
+                placeholder={
+                  definition.default_value !== undefined &&
+                  definition.default_value !== null
+                    ? `Default: ${customFieldInputText(definition.default_value)}`
+                    : "Optional"
+                }
+                rows={definition.field_type === "text_long" ? 3 : 4}
+                disabled={disabled}
+              />
+            ) : (
+              <Input
+                type={
+                  definition.field_type === "integer" ||
+                  definition.field_type === "decimal"
+                    ? "number"
+                    : definition.field_type === "date"
+                      ? "date"
+                      : definition.field_type === "date_time"
+                        ? "datetime-local"
+                        : definition.field_type === "url"
+                          ? "url"
+                          : "text"
+                }
+                step={definition.field_type === "decimal" ? "any" : undefined}
+                value={customFieldInputText(fieldValue)}
+                onChange={(event) => {
+                  const nextFieldValue = parseCustomFieldInputValue(
+                    definition,
+                    event.target.value,
+                  );
+                  setValues((prev) => ({
+                    ...prev,
+                    [definition.field_key]: nextFieldValue,
+                  }));
+                }}
+                placeholder={
+                  definition.default_value !== undefined &&
+                  definition.default_value !== null
+                    ? `Default: ${customFieldInputText(definition.default_value)}`
+                    : "Optional"
+                }
+                disabled={disabled}
+              />
+            )}
+
+            {definition.description ? (
+              <p className="text-xs text-slate-500">{definition.description}</p>
+            ) : null}
+          </div>
+        );
+      })}
+    </div>
+  );
+}
diff --git a/frontend/src/app/boards/[boardId]/custom-field-utils.test.tsx b/frontend/src/app/boards/[boardId]/custom-field-utils.test.tsx
new file mode 100644
index 00000000..1c5f05c5
--- /dev/null
+++ b/frontend/src/app/boards/[boardId]/custom-field-utils.test.tsx
@@ -0,0 +1,150 @@
+import { describe, expect, it } from "vitest";
+import { render, screen } from "@testing-library/react";
+
+import type { TaskCustomFieldDefinitionRead } from "@/api/generated/model";
+import {
+  boardCustomFieldValues,
+  canonicalizeCustomFieldValues,
+  customFieldPayload,
+  customFieldPatchPayload,
+  firstMissingRequiredCustomField,
+  formatCustomFieldDetailValue,
+  isCustomFieldVisible,
+  parseCustomFieldInputValue,
+  type TaskCustomFieldValues,
+} from "./custom-field-utils";
+
+const buildDefinition = (
+  overrides: Partial<TaskCustomFieldDefinitionRead> = {},
+): TaskCustomFieldDefinitionRead => ({
+  id: "field-1",
+  organization_id: "org-1",
+  field_key: "client_name",
+  field_type: "text",
+  ui_visibility: "always",
+  label: "Client name",
+  required: false,
+  default_value: null,
+  description: null,
+  validation_regex: null,
+  board_ids: ["board-1"],
+  created_at: "2026-01-01T00:00:00Z",
+  updated_at: "2026-01-01T00:00:00Z",
+  ...overrides,
+});
+
+describe("custom-field-utils", () => {
+  it("normalizes board field values with defaults", () => {
+    const definitions = [
+      buildDefinition({ field_key: "priority", default_value: "medium" }),
+      buildDefinition({
+        id: "field-2",
+        field_key: "estimate",
+        default_value: 1,
+      }),
+    ];
+
+    expect(boardCustomFieldValues(definitions, { priority: "high" })).toEqual({
+      priority: "high",
+      estimate: 1,
+    });
+  });
+
+  it("builds payload and patch payload with only changed keys", () => {
+    const definitions = [
+      buildDefinition({ field_key: "priority" }),
+      buildDefinition({
+        id: "field-2",
+        field_key: "estimate",
+        field_type: "integer",
+      }),
+    ];
+    const currentValues: TaskCustomFieldValues = {
+      priority: "high",
+      estimate: 2,
+    };
+    const nextPayload = customFieldPayload(definitions, {
+      priority: "high",
+      estimate: 3,
+    });
+
+    expect(nextPayload).toEqual({ priority: "high", estimate: 3 });
+    expect(
+      customFieldPatchPayload(definitions, currentValues, nextPayload),
+    ).toEqual({
+      estimate: 3,
+    });
+  });
+
+  it("finds the first missing required custom field", () => {
+    const definitions = [
+      buildDefinition({
+        field_key: "required_a",
+        label: "Required A",
+        required: true,
+      }),
+      buildDefinition({
+        id: "field-2",
+        field_key: "required_b",
+        label: "Required B",
+        required: true,
+      }),
+    ];
+
+    expect(
+      firstMissingRequiredCustomField(definitions, { required_a: "value" }),
+    ).toBe("Required B");
+  });
+
+  it("parses typed custom-field input values", () => {
+    expect(
+      parseCustomFieldInputValue(
+        buildDefinition({ field_type: "integer" }),
+        "42",
+      ),
+    ).toBe(42);
+    expect(
+      parseCustomFieldInputValue(
+        buildDefinition({ field_type: "boolean" }),
+        "false",
+      ),
+    ).toBe(false);
+    expect(
+      parseCustomFieldInputValue(
+        buildDefinition({ field_type: "json" }),
+        '{"a":1}',
+      ),
+    ).toEqual({ a: 1 });
+  });
+
+  it("handles visibility and canonicalization", () => {
+    expect(
+      isCustomFieldVisible(
+        buildDefinition({ ui_visibility: "hidden" }),
+        "value",
+      ),
+    ).toBe(false);
+    expect(
+      isCustomFieldVisible(buildDefinition({ ui_visibility: "if_set" }), ""),
+    ).toBe(false);
+    expect(canonicalizeCustomFieldValues({ b: 2, a: { z: 1, y: 2 } })).toBe(
+      canonicalizeCustomFieldValues({ a: { y: 2, z: 1 }, b: 2 }),
+    );
+  });
+
+  it("renders url detail values as links", () => {
+    const definition = buildDefinition({
+      field_type: "url",
+      field_key: "website",
+    });
+    const node = formatCustomFieldDetailValue(
+      definition,
+      "https://example.com",
+    );
+    render(<>{node}</>);
+
+    expect(
+      screen.getByRole("link", { name: /https:\/\/example.com/i }),
+    ).toHaveAttribute("href", "https://example.com/");
+  });
+});
diff --git a/frontend/src/app/boards/[boardId]/custom-field-utils.tsx b/frontend/src/app/boards/[boardId]/custom-field-utils.tsx
new file mode 100644
index 00000000..a9ffb265
--- /dev/null
+++ b/frontend/src/app/boards/[boardId]/custom-field-utils.tsx
@@ -0,0 +1,329 @@
+import type { ReactNode } from "react";
+import { ArrowUpRight } from "lucide-react";
+
+import type { TaskCustomFieldDefinitionRead } from "@/api/generated/model";
+import { parseApiDatetime } from "@/lib/datetime";
+
+export type TaskCustomFieldValues = Record<string, unknown>;
+
+const isRecordObject = (value: unknown): value is Record<string, unknown> =>
+  !!value && typeof value === "object" && !Array.isArray(value);
+
+export const normalizeCustomFieldValues = (
+  value: unknown,
+): TaskCustomFieldValues => {
+  if (!isRecordObject(value)) return {};
+  const entries = Object.entries(value);
+  if (entries.length === 0) return {};
+  return entries
+    .sort(([left], [right]) => left.localeCompare(right))
+    .reduce((acc, [key, rawValue]) => {
+      if (isRecordObject(rawValue)) {
+        acc[key] = normalizeCustomFieldValues(rawValue);
+        return acc;
+      }
+      if (Array.isArray(rawValue)) {
+        acc[key] = rawValue.map((item) =>
+          isRecordObject(item) ? normalizeCustomFieldValues(item) : item,
+        );
+        return acc;
+      }
+      acc[key] = rawValue;
+      return acc;
+    }, {} as TaskCustomFieldValues);
+};
+
+export const canonicalizeCustomFieldValues = (value: unknown): string =>
+  JSON.stringify(normalizeCustomFieldValues(value));
+
+export const customFieldInputText = (value: unknown): string => {
+  if (value === null || value === undefined) return "";
+  if (typeof value === "string") return value;
+  try {
+    return JSON.stringify(value);
+  } catch {
+    return String(value);
+  }
+};
+
+const formatDateOnlyValue = (value: string): string => {
+  const trimmed = value.trim();
+  const match = /^(\d{4})-(\d{2})-(\d{2})$/.exec(trimmed);
+  if (match) {
+    const year = Number.parseInt(match[1], 10);
+    const month = Number.parseInt(match[2], 10);
+    const day = Number.parseInt(match[3], 10);
+    const parsed = new Date(year, month - 1, day);
+    if (
+      parsed.getFullYear() === year &&
+      parsed.getMonth() === month - 1 &&
+      parsed.getDate() === day
+    ) {
+      return parsed.toLocaleDateString(undefined, {
+        year: "numeric",
+        month: "short",
+        day: "numeric",
+      });
+    }
+  }
+  const parsed = new Date(trimmed);
+  if (Number.isNaN(parsed.getTime())) return trimmed;
+  return parsed.toLocaleDateString(undefined, {
+    year: "numeric",
+    month: "short",
+    day: "numeric",
+  });
+};
+
+const formatDateTimeValue = (value: string): string => {
+  const parsed = parseApiDatetime(value) ?? new Date(value);
+  if (Number.isNaN(parsed.getTime())) return value;
+  return parsed.toLocaleString(undefined, {
+    year: "numeric",
+    month: "short",
+    day: "numeric",
+    hour: "2-digit",
+    minute: "2-digit",
+  });
+};
+
+export const formatCustomFieldDetailValue = (
+  definition: TaskCustomFieldDefinitionRead,
+  value: unknown,
+): ReactNode => {
+  if (value === null || value === undefined) return "—";
+
+  const fieldType = definition.field_type ?? "text";
+  if (fieldType === "boolean") {
+    if (value === true) return "True";
+    if (value === false) return "False";
+    if (typeof value === "string") {
+      const normalized = value.trim().toLowerCase();
+      if (normalized === "true") return "True";
+      if (normalized === "false") return "False";
+    }
+    return customFieldInputText(value) || "—";
+  }
+
+  if (fieldType === "integer" || fieldType === "decimal") {
+    if (typeof value === "number" && Number.isFinite(value)) {
+      return value.toLocaleString();
+    }
+    if (typeof value === "string") {
+      const trimmed = value.trim();
+      if (!trimmed) return "—";
+      const parsed = Number(trimmed);
+      if (Number.isFinite(parsed)) return parsed.toLocaleString();
+      return trimmed;
+    }
+    return customFieldInputText(value) || "—";
+  }
+
+  if (fieldType === "date") {
+    if (typeof value !== "string") return customFieldInputText(value) || "—";
+    if (!value.trim()) return "—";
+    return formatDateOnlyValue(value);
+  }
+
+  if (fieldType === "date_time") {
+    if (typeof value !== "string") return customFieldInputText(value) || "—";
+    if (!value.trim()) return "—";
+    return formatDateTimeValue(value);
+  }
+
+  if (fieldType === "url") {
+    if (typeof value !== "string") return customFieldInputText(value) || "—";
+    const trimmed = value.trim();
+    if (!trimmed) return "—";
+    try {
+      const parsedUrl = new URL(trimmed);
+      return (
+        <a
+          href={parsedUrl.toString()}
+          target="_blank"
+          rel="noreferrer"
+          className="inline-flex items-center gap-1 text-blue-700 underline decoration-blue-300 underline-offset-2 hover:text-blue-800"
+        >
+          <span className="break-all">{parsedUrl.toString()}</span>
+          <ArrowUpRight className="h-3.5 w-3.5 flex-shrink-0" />
+        </a>
+      );
+    } catch {
+      return trimmed;
+    }
+  }
+
+  if (fieldType === "json") {
+    try {
+      const normalized = typeof value === "string" ? JSON.parse(value) : value;
+      return (
+        <pre className="whitespace-pre-wrap break-words rounded border border-slate-200 bg-white px-2 py-1 font-mono text-xs leading-relaxed text-slate-800">
+          {JSON.stringify(normalized, null, 2)}
+        </pre>
+      );
+    } catch {
+      return customFieldInputText(value) || "—";
+    }
+  }
+
+  if (fieldType === "text_long") {
+    const text = customFieldInputText(value);
+    return text ? (
+      <span className="whitespace-pre-wrap break-words">{text}</span>
+    ) : (
+      "—"
+    );
+  }
+
+  return customFieldInputText(value) || "—";
+};
+
+const isCustomFieldValueSet = (value: unknown): boolean => {
+  if (value === null || value === undefined) return false;
+  if (typeof value === "string") return value.trim().length > 0;
+  if (Array.isArray(value)) return value.length > 0;
+  if (isRecordObject(value)) return Object.keys(value).length > 0;
+  return true;
+};
+
+export const isCustomFieldVisible = (
+  definition: TaskCustomFieldDefinitionRead,
+  value: unknown,
+): boolean => {
+  if (definition.ui_visibility === "hidden") return false;
+  if (definition.ui_visibility === "if_set")
+    return isCustomFieldValueSet(value);
+  return true;
+};
+
+export const parseCustomFieldInputValue = (
+  definition: TaskCustomFieldDefinitionRead,
+  text: string,
+): unknown | null => {
+  const trimmed = text.trim();
+  if (!trimmed) return null;
+  if (
+    definition.field_type === "text" ||
+    definition.field_type === "text_long"
+  ) {
+    return trimmed;
+  }
+  if (definition.field_type === "integer") {
+    if (!/^-?\d+$/.test(trimmed)) return trimmed;
+    return Number.parseInt(trimmed, 10);
+  }
+  if (definition.field_type === "decimal") {
+    if (!/^-?\d+(\.\d+)?$/.test(trimmed)) return trimmed;
+    return Number.parseFloat(trimmed);
+  }
+  if (definition.field_type === "boolean") {
+    if (trimmed.toLowerCase() === "true") return true;
+    if (trimmed.toLowerCase() === "false") return false;
+    return trimmed;
+  }
+  if (
+    definition.field_type === "date" ||
+    definition.field_type === "date_time" ||
+    definition.field_type === "url"
+  ) {
+    return trimmed;
+  }
+  if (definition.field_type === "json") {
+    try {
+      const parsed = JSON.parse(trimmed);
+      if (parsed === null || typeof parsed !== "object") {
+        return trimmed;
+      }
+      return parsed;
+    } catch {
+      return trimmed;
+    }
+  }
+  try {
+    return JSON.parse(trimmed);
+  } catch {
+    return trimmed;
+  }
+};
+
+export const boardCustomFieldValues = (
+  definitions: TaskCustomFieldDefinitionRead[],
+  value: unknown,
+): TaskCustomFieldValues => {
+  const source = normalizeCustomFieldValues(value);
+  return definitions.reduce((acc, definition) => {
+    const key = definition.field_key;
+    if (Object.prototype.hasOwnProperty.call(source, key)) {
+      acc[key] = source[key];
+      return acc;
+    }
+    acc[key] = definition.default_value ?? null;
+    return acc;
+  }, {} as TaskCustomFieldValues);
+};
+
+export const customFieldPayload = (
+  definitions: TaskCustomFieldDefinitionRead[],
+  values: TaskCustomFieldValues,
+): TaskCustomFieldValues =>
+  definitions.reduce((acc, definition) => {
+    const key = definition.field_key;
+    acc[key] =
+      Object.prototype.hasOwnProperty.call(values, key) &&
+      values[key] !== undefined
+        ? values[key]
+        : null;
+    return acc;
+  }, {} as TaskCustomFieldValues);
+
+const canonicalizeCustomFieldValue = (value: unknown): string => {
+  if (value === undefined) return "__undefined__";
+  if (value === null) return "__null__";
+  if (isRecordObject(value)) {
+    return JSON.stringify(normalizeCustomFieldValues(value));
+  }
+  try {
+    return JSON.stringify(value);
+  } catch {
+    return String(value);
+  }
+};
+
+export const customFieldPatchPayload = (
+  definitions: TaskCustomFieldDefinitionRead[],
+  currentValues: TaskCustomFieldValues,
+  nextValues: TaskCustomFieldValues,
+): TaskCustomFieldValues =>
+  definitions.reduce((acc, definition) => {
+    const key = definition.field_key;
+    const currentValue = Object.prototype.hasOwnProperty.call(
+      currentValues,
+      key,
+    )
+      ? currentValues[key]
+      : null;
+    const nextValue = Object.prototype.hasOwnProperty.call(nextValues, key)
+      ? nextValues[key]
+      : null;
+    if (
+      canonicalizeCustomFieldValue(currentValue) ===
+      canonicalizeCustomFieldValue(nextValue)
+    ) {
+      return acc;
+    }
+    acc[key] = nextValue ?? null;
+    return acc;
+  }, {} as TaskCustomFieldValues);
+
+export const firstMissingRequiredCustomField = (
+  definitions: TaskCustomFieldDefinitionRead[],
+  values: TaskCustomFieldValues,
+): string | null => {
+  for (const definition of definitions) {
+    if (definition.required !== true) continue;
+    const value = values[definition.field_key];
+    if (value !== null && value !== undefined) continue;
+    return definition.label || definition.field_key;
+  }
+  return null;
+};
diff --git a/frontend/src/app/boards/[boardId]/page.tsx b/frontend/src/app/boards/[boardId]/page.tsx
index 01c95282..53b176bc 100644
--- a/frontend/src/app/boards/[boardId]/page.tsx
+++ b/frontend/src/app/boards/[boardId]/page.tsx
@@ -2,15 +2,7 @@
 
 export const dynamic = "force-dynamic";
 
-import {
-  memo,
-  type ReactNode,
-  useCallback,
-  useEffect,
-  useMemo,
-  useRef,
-  useState,
-} from "react";
+import { memo, useCallback, useEffect, useMemo, useRef, useState } from "react";
 import { useParams, useRouter, useSearchParams } from "next/navigation";
 
 import { SignInButton, SignedIn, SignedOut, useAuth } from "@/auth/clerk";
@@ -38,6 +30,7 @@ import {
 } from "@/components/molecules/DependencyBanner";
 import { DashboardShell } from "@/components/templates/DashboardShell";
 import { BoardChatComposer } from "@/components/BoardChatComposer";
+import { TaskCustomFieldsEditor } from "./TaskCustomFieldsEditor";
 import { Button } from "@/components/ui/button";
 import {
   Dialog,
@@ -117,11 +110,20 @@ import {
 } from "@/lib/datetime";
 import { cn } from "@/lib/utils";
 import { usePageActive } from "@/hooks/usePageActive";
+import {
+  boardCustomFieldValues,
+  canonicalizeCustomFieldValues,
+  customFieldPayload,
+  customFieldPatchPayload,
+  firstMissingRequiredCustomField,
+  formatCustomFieldDetailValue,
+  isCustomFieldVisible,
+  type TaskCustomFieldValues,
+} from "./custom-field-utils";
 
 type Board = BoardRead;
 
 type TaskStatus = Exclude<TaskCardRead["status"], undefined>;
-type TaskCustomFieldValues = Record<string, unknown>;
 
 type TaskCustomFieldPayload = {
   custom_field_values?: TaskCustomFieldValues;
@@ -452,330 +454,6 @@ const normalizeTask = (task: TaskCardRead): Task => ({
   approvals_pending_count: task.approvals_pending_count ?? 0,
 });
 
-const isRecordObject = (value: unknown): value is Record<string, unknown> =>
-  !!value && typeof value === "object" && !Array.isArray(value);
-
-const normalizeCustomFieldValues = (value: unknown): TaskCustomFieldValues => {
-  if (!isRecordObject(value)) return {};
-  const entries = Object.entries(value);
-  if (entries.length === 0) return {};
-  return entries
-    .sort(([left], [right]) => left.localeCompare(right))
-    .reduce((acc, [key, rawValue]) => {
-      if (isRecordObject(rawValue)) {
-        acc[key] = normalizeCustomFieldValues(rawValue);
-        return acc;
-      }
-      if (Array.isArray(rawValue)) {
-        acc[key] = rawValue.map((item) =>
-          isRecordObject(item) ? normalizeCustomFieldValues(item) : item,
-        );
-        return acc;
-      }
-      acc[key] = rawValue;
-      return acc;
-    }, {} as TaskCustomFieldValues);
-};
-
-const canonicalizeCustomFieldValues = (value: unknown): string =>
-  JSON.stringify(normalizeCustomFieldValues(value));
-
-const customFieldInputText = (value: unknown): string => {
-  if (value === null || value === undefined) return "";
-  if (typeof value === "string") return value;
-  try {
-    return JSON.stringify(value);
-  } catch {
-    return String(value);
-  }
-};
-
-const formatDateOnlyValue = (value: string): string => {
-  const trimmed = value.trim();
-  const match = /^(\d{4})-(\d{2})-(\d{2})$/.exec(trimmed);
-  if (match) {
-    const year = Number.parseInt(match[1], 10);
-    const month = Number.parseInt(match[2], 10);
-    const day = Number.parseInt(match[3], 10);
-    const parsed = new Date(year, month - 1, day);
-    if (
-      parsed.getFullYear() === year &&
-      parsed.getMonth() === month - 1 &&
-      parsed.getDate() === day
-    ) {
-      return parsed.toLocaleDateString(undefined, {
-        year: "numeric",
-        month: "short",
-        day: "numeric",
-      });
-    }
-  }
-  const parsed = new Date(trimmed);
-  if (Number.isNaN(parsed.getTime())) return trimmed;
-  return parsed.toLocaleDateString(undefined, {
-    year: "numeric",
-    month: "short",
-    day: "numeric",
-  });
-};
-
-const formatDateTimeValue = (value: string): string => {
-  const parsed = parseApiDatetime(value) ?? new Date(value);
-  if (Number.isNaN(parsed.getTime())) return value;
-  return parsed.toLocaleString(undefined, {
-    year: "numeric",
-    month: "short",
-    day: "numeric",
-    hour: "2-digit",
-    minute: "2-digit",
-  });
-};
-
-const formatCustomFieldDetailValue = (
-  definition: TaskCustomFieldDefinitionRead,
-  value: unknown,
-): ReactNode => {
-  if (value === null || value === undefined) return "—";
-
-  const fieldType = definition.field_type ?? "text";
-  if (fieldType === "boolean") {
-    if (value === true) return "True";
-    if (value === false) return "False";
-    if (typeof value === "string") {
-      const normalized = value.trim().toLowerCase();
-      if (normalized === "true") return "True";
-      if (normalized === "false") return "False";
-    }
-    return customFieldInputText(value) || "—";
-  }
-
-  if (fieldType === "integer" || fieldType === "decimal") {
-    if (typeof value === "number" && Number.isFinite(value)) {
-      return value.toLocaleString();
-    }
-    if (typeof value === "string") {
-      const trimmed = value.trim();
-      if (!trimmed) return "—";
-      const parsed = Number(trimmed);
-      if (Number.isFinite(parsed)) return parsed.toLocaleString();
-      return trimmed;
-    }
-    return customFieldInputText(value) || "—";
-  }
-
-  if (fieldType === "date") {
-    if (typeof value !== "string") return customFieldInputText(value) || "—";
-    if (!value.trim()) return "—";
-    return formatDateOnlyValue(value);
-  }
-
-  if (fieldType === "date_time") {
-    if (typeof value !== "string") return customFieldInputText(value) || "—";
-    if (!value.trim()) return "—";
-    return formatDateTimeValue(value);
-  }
-
-  if (fieldType === "url") {
-    if (typeof value !== "string") return customFieldInputText(value) || "—";
-    const trimmed = value.trim();
-    if (!trimmed) return "—";
-    try {
-      const parsedUrl = new URL(trimmed);
-      return (
-        <a
-          href={parsedUrl.toString()}
-          target="_blank"
-          rel="noreferrer"
-          className="inline-flex items-center gap-1 text-blue-700 underline decoration-blue-300 underline-offset-2 hover:text-blue-800"
-        >
-          <span className="break-all">{parsedUrl.toString()}</span>
-          <ArrowUpRight className="h-3.5 w-3.5 flex-shrink-0" />
-        </a>
-      );
-    } catch {
-      return trimmed;
-    }
-  }
-
-  if (fieldType === "json") {
-    try {
-      const normalized = typeof value === "string" ? JSON.parse(value) : value;
-      return (
-        <pre className="whitespace-pre-wrap break-words rounded border border-slate-200 bg-white px-2 py-1 font-mono text-xs leading-relaxed text-slate-800">
-          {JSON.stringify(normalized, null, 2)}
-        </pre>
-      );
-    } catch {
-      return customFieldInputText(value) || "—";
-    }
-  }
-
-  if (fieldType === "text_long") {
-    const text = customFieldInputText(value);
-    return text ? (
-      <span className="whitespace-pre-wrap break-words">{text}</span>
-    ) : (
-      "—"
-    );
-  }
-
-  return customFieldInputText(value) || "—";
-};
-
-const isCustomFieldValueSet = (value: unknown): boolean => {
-  if (value === null || value === undefined) return false;
-  if (typeof value === "string") return value.trim().length > 0;
-  if (Array.isArray(value)) return value.length > 0;
-  if (isRecordObject(value)) return Object.keys(value).length > 0;
-  return true;
-};
-
-const isCustomFieldVisible = (
-  definition: TaskCustomFieldDefinitionRead,
-  value: unknown,
-): boolean => {
-  if (definition.ui_visibility === "hidden") return false;
-  if (definition.ui_visibility === "if_set")
-    return isCustomFieldValueSet(value);
-  return true;
-};
-
-const parseCustomFieldInputValue = (
-  definition: TaskCustomFieldDefinitionRead,
-  text: string,
-): unknown | null => {
-  const trimmed = text.trim();
-  if (!trimmed) return null;
-  if (
-    definition.field_type === "text" ||
-    definition.field_type === "text_long"
-  ) {
-    return trimmed;
-  }
-  if (definition.field_type === "integer") {
-    if (!/^-?\d+$/.test(trimmed)) return trimmed;
-    return Number.parseInt(trimmed, 10);
-  }
-  if (definition.field_type === "decimal") {
-    if (!/^-?\d+(\.\d+)?$/.test(trimmed)) return trimmed;
-    return Number.parseFloat(trimmed);
-  }
-  if (definition.field_type === "boolean") {
-    if (trimmed.toLowerCase() === "true") return true;
-    if (trimmed.toLowerCase() === "false") return false;
-    return trimmed;
-  }
-  if (
-    definition.field_type === "date" ||
-    definition.field_type === "date_time" ||
-    definition.field_type === "url"
-  ) {
-    return trimmed;
-  }
-  if (definition.field_type === "json") {
-    try {
-      const parsed = JSON.parse(trimmed);
-      if (
-        parsed === null ||
-        typeof parsed !== "object" ||
-        (!Array.isArray(parsed) && typeof parsed !== "object")
-      ) {
-        return trimmed;
-      }
-      return parsed;
-    } catch {
-      return trimmed;
-    }
-  }
-  try {
-    return JSON.parse(trimmed);
-  } catch {
-    return trimmed;
-  }
-};
-
-const boardCustomFieldValues = (
-  definitions: TaskCustomFieldDefinitionRead[],
-  value: unknown,
-): TaskCustomFieldValues => {
-  const source = normalizeCustomFieldValues(value);
-  return definitions.reduce((acc, definition) => {
-    const key = definition.field_key;
-    if (Object.prototype.hasOwnProperty.call(source, key)) {
-      acc[key] = source[key];
-      return acc;
-    }
-    acc[key] = definition.default_value ?? null;
-    return acc;
-  }, {} as TaskCustomFieldValues);
-};
-
-const customFieldPayload = (
-  definitions: TaskCustomFieldDefinitionRead[],
-  values: TaskCustomFieldValues,
-): TaskCustomFieldValues =>
-  definitions.reduce((acc, definition) => {
-    const key = definition.field_key;
-    acc[key] =
-      Object.prototype.hasOwnProperty.call(values, key) &&
-      values[key] !== undefined
-        ? values[key]
-        : null;
-    return acc;
-  }, {} as TaskCustomFieldValues);
-
-const canonicalizeCustomFieldValue = (value: unknown): string => {
-  if (value === undefined) return "__undefined__";
-  if (value === null) return "__null__";
-  if (isRecordObject(value)) {
-    return JSON.stringify(normalizeCustomFieldValues(value));
-  }
-  try {
-    return JSON.stringify(value);
-  } catch {
-    return String(value);
-  }
-};
-
-const customFieldPatchPayload = (
-  definitions: TaskCustomFieldDefinitionRead[],
-  currentValues: TaskCustomFieldValues,
-  nextValues: TaskCustomFieldValues,
-): TaskCustomFieldValues =>
-  definitions.reduce((acc, definition) => {
-    const key = definition.field_key;
-    const currentValue = Object.prototype.hasOwnProperty.call(
-      currentValues,
-      key,
-    )
-      ? currentValues[key]
-      : null;
-    const nextValue = Object.prototype.hasOwnProperty.call(nextValues, key)
-      ? nextValues[key]
-      : null;
-    if (
-      canonicalizeCustomFieldValue(currentValue) ===
-      canonicalizeCustomFieldValue(nextValue)
-    ) {
-      return acc;
-    }
-    acc[key] = nextValue ?? null;
-    return acc;
-  }, {} as TaskCustomFieldValues);
-
-const firstMissingRequiredCustomField = (
-  definitions: TaskCustomFieldDefinitionRead[],
-  values: TaskCustomFieldValues,
-): string | null => {
-  for (const definition of definitions) {
-    if (definition.required !== true) continue;
-    const value = values[definition.field_key];
-    if (value !== null && value !== undefined) continue;
-    return definition.label || definition.field_key;
-  }
-  return null;
-};
-
 const normalizeAgent = (agent: AgentRead): Agent => ({
   ...agent,
   status: agent.status ?? "offline",
@@ -4345,133 +4023,13 @@ export default function BoardDetailPage() {
               <label className="text-xs font-semibold uppercase tracking-wider text-slate-500">
                 Custom fields
               </label>
-              {customFieldDefinitionsQuery.isLoading ? (
-                <p className="text-xs text-slate-500">Loading custom fields…</p>
-              ) : boardCustomFieldDefinitions.length === 0 ? (
-                <p className="text-xs text-slate-500">
-                  No custom fields configured for this board.
-                </p>
-              ) : (
-                <div className="space-y-3">
-                  {boardCustomFieldDefinitions.map((definition) => {
-                    const fieldValue =
-                      editCustomFieldValues[definition.field_key];
-                    if (!isCustomFieldVisible(definition, fieldValue)) {
-                      return null;
-                    }
-                    return (
-                      <div key={definition.id} className="space-y-1">
-                        <label className="text-[11px] font-semibold uppercase tracking-wide text-slate-500">
-                          {definition.label || definition.field_key}
-                          {definition.required === true ? (
-                            <span className="ml-1 text-rose-600">*</span>
-                          ) : null}
-                        </label>
-                        {definition.field_type === "boolean" ? (
-                          <Select
-                            value={
-                              fieldValue === true
-                                ? "true"
-                                : fieldValue === false
-                                  ? "false"
-                                  : "unset"
-                            }
-                            onValueChange={(value) =>
-                              setEditCustomFieldValues((prev) => ({
-                                ...prev,
-                                [definition.field_key]:
-                                  value === "unset" ? null : value === "true",
-                              }))
-                            }
-                            disabled={
-                              !selectedTask || isSavingTask || !canWrite
-                            }
-                          >
-                            <SelectTrigger>
-                              <SelectValue placeholder="Optional" />
-                            </SelectTrigger>
-                            <SelectContent>
-                              <SelectItem value="unset">Optional</SelectItem>
-                              <SelectItem value="true">True</SelectItem>
-                              <SelectItem value="false">False</SelectItem>
-                            </SelectContent>
-                          </Select>
-                        ) : definition.field_type === "text_long" ||
-                          definition.field_type === "json" ? (
-                          <Textarea
-                            value={customFieldInputText(fieldValue)}
-                            onChange={(event) =>
-                              setEditCustomFieldValues((prev) => ({
-                                ...prev,
-                                [definition.field_key]:
-                                  parseCustomFieldInputValue(
-                                    definition,
-                                    event.target.value,
-                                  ),
-                              }))
-                            }
-                            placeholder={
-                              definition.default_value !== undefined &&
-                              definition.default_value !== null
-                                ? `Default: ${customFieldInputText(definition.default_value)}`
-                                : "Optional"
-                            }
-                            rows={definition.field_type === "text_long" ? 3 : 4}
-                            disabled={
-                              !selectedTask || isSavingTask || !canWrite
-                            }
-                          />
-                        ) : (
-                          <Input
-                            type={
-                              definition.field_type === "integer" ||
-                              definition.field_type === "decimal"
-                                ? "number"
-                                : definition.field_type === "date"
-                                  ? "date"
-                                  : definition.field_type === "date_time"
-                                    ? "datetime-local"
-                                    : definition.field_type === "url"
-                                      ? "url"
-                                      : "text"
-                            }
-                            step={
-                              definition.field_type === "decimal"
-                                ? "any"
-                                : undefined
-                            }
-                            value={customFieldInputText(fieldValue)}
-                            onChange={(event) =>
-                              setEditCustomFieldValues((prev) => ({
-                                ...prev,
-                                [definition.field_key]:
-                                  parseCustomFieldInputValue(
-                                    definition,
-                                    event.target.value,
-                                  ),
-                              }))
-                            }
-                            placeholder={
-                              definition.default_value !== undefined &&
-                              definition.default_value !== null
-                                ? `Default: ${customFieldInputText(definition.default_value)}`
-                                : "Optional"
-                            }
-                            disabled={
-                              !selectedTask || isSavingTask || !canWrite
-                            }
-                          />
-                        )}
-                        {definition.description ? (
-                          <p className="text-xs text-slate-500">
-                            {definition.description}
-                          </p>
-                        ) : null}
-                      </div>
-                    );
-                  })}
-                </div>
-              )}
+              <TaskCustomFieldsEditor
+                definitions={boardCustomFieldDefinitions}
+                values={editCustomFieldValues}
+                setValues={setEditCustomFieldValues}
+                isLoading={customFieldDefinitionsQuery.isLoading}
+                disabled={!selectedTask || isSavingTask || !canWrite}
+              />
             </div>
             <div className="grid gap-4 md:grid-cols-2">
               <div className="space-y-2">
@@ -4801,127 +4359,13 @@ export default function BoardDetailPage() {
               <label className="text-sm font-medium text-strong">
                 Custom fields
               </label>
-              {customFieldDefinitionsQuery.isLoading ? (
-                <p className="text-xs text-slate-500">Loading custom fields…</p>
-              ) : boardCustomFieldDefinitions.length === 0 ? (
-                <p className="text-xs text-slate-500">
-                  No custom fields configured for this board.
-                </p>
-              ) : (
-                <div className="space-y-3">
-                  {boardCustomFieldDefinitions.map((definition) => {
-                    const fieldValue =
-                      createCustomFieldValues[definition.field_key];
-                    if (!isCustomFieldVisible(definition, fieldValue)) {
-                      return null;
-                    }
-                    return (
-                      <div key={definition.id} className="space-y-1">
-                        <label className="text-[11px] font-semibold uppercase tracking-wide text-slate-500">
-                          {definition.label || definition.field_key}
-                          {definition.required === true ? (
-                            <span className="ml-1 text-rose-600">*</span>
-                          ) : null}
-                        </label>
-                        {definition.field_type === "boolean" ? (
-                          <Select
-                            value={
-                              fieldValue === true
-                                ? "true"
-                                : fieldValue === false
-                                  ? "false"
-                                  : "unset"
-                            }
-                            onValueChange={(value) =>
-                              setCreateCustomFieldValues((prev) => ({
-                                ...prev,
-                                [definition.field_key]:
-                                  value === "unset" ? null : value === "true",
-                              }))
-                            }
-                            disabled={!canWrite || isCreating}
-                          >
-                            <SelectTrigger>
-                              <SelectValue placeholder="Optional" />
-                            </SelectTrigger>
-                            <SelectContent>
-                              <SelectItem value="unset">Optional</SelectItem>
-                              <SelectItem value="true">True</SelectItem>
-                              <SelectItem value="false">False</SelectItem>
-                            </SelectContent>
-                          </Select>
-                        ) : definition.field_type === "text_long" ||
-                          definition.field_type === "json" ? (
-                          <Textarea
-                            value={customFieldInputText(fieldValue)}
-                            onChange={(event) =>
-                              setCreateCustomFieldValues((prev) => ({
-                                ...prev,
-                                [definition.field_key]:
-                                  parseCustomFieldInputValue(
-                                    definition,
-                                    event.target.value,
-                                  ),
-                              }))
-                            }
-                            placeholder={
-                              definition.default_value !== undefined &&
-                              definition.default_value !== null
-                                ? `Default: ${customFieldInputText(definition.default_value)}`
-                                : "Optional"
-                            }
-                            rows={definition.field_type === "text_long" ? 3 : 4}
-                            disabled={!canWrite || isCreating}
-                          />
-                        ) : (
-                          <Input
-                            type={
-                              definition.field_type === "integer" ||
-                              definition.field_type === "decimal"
-                                ? "number"
-                                : definition.field_type === "date"
-                                  ? "date"
-                                  : definition.field_type === "date_time"
-                                    ? "datetime-local"
-                                    : definition.field_type === "url"
-                                      ? "url"
-                                      : "text"
-                            }
-                            step={
-                              definition.field_type === "decimal"
-                                ? "any"
-                                : undefined
-                            }
-                            value={customFieldInputText(fieldValue)}
-                            onChange={(event) =>
-                              setCreateCustomFieldValues((prev) => ({
-                                ...prev,
-                                [definition.field_key]:
-                                  parseCustomFieldInputValue(
-                                    definition,
-                                    event.target.value,
-                                  ),
-                              }))
-                            }
-                            placeholder={
-                              definition.default_value !== undefined &&
-                              definition.default_value !== null
-                                ? `Default: ${customFieldInputText(definition.default_value)}`
-                                : "Optional"
-                            }
-                            disabled={!canWrite || isCreating}
-                          />
-                        )}
-                        {definition.description ? (
-                          <p className="text-xs text-slate-500">
-                            {definition.description}
-                          </p>
-                        ) : null}
-                      </div>
-                    );
-                  })}
-                </div>
-              )}
+              <TaskCustomFieldsEditor
+                definitions={boardCustomFieldDefinitions}
+                values={createCustomFieldValues}
+                setValues={setCreateCustomFieldValues}
+                isLoading={customFieldDefinitionsQuery.isLoading}
+                disabled={!canWrite || isCreating}
+              />
             </div>
             <div className="space-y-2">
               <label className="text-sm font-medium text-strong">
diff --git a/frontend/src/app/custom-fields/[fieldId]/edit/page.tsx b/frontend/src/app/custom-fields/[fieldId]/edit/page.tsx
index cd287a40..8d9ca41e 100644
--- a/frontend/src/app/custom-fields/[fieldId]/edit/page.tsx
+++ b/frontend/src/app/custom-fields/[fieldId]/edit/page.tsx
@@ -2,8 +2,7 @@
 
 export const dynamic = "force-dynamic";
 
-import { type FormEvent, useMemo, useState } from "react";
-import Link from "next/link";
+import { useMemo } from "react";
 import { useParams, useRouter } from "next/navigation";
 
 import { useAuth } from "@/auth/clerk";
@@ -20,521 +19,17 @@ import {
   useListOrgCustomFieldsApiV1OrganizationsMeCustomFieldsGet,
   useUpdateOrgCustomFieldApiV1OrganizationsMeCustomFieldsTaskCustomFieldDefinitionIdPatch,
 } from "@/api/generated/org-custom-fields/org-custom-fields";
-import type {
-  BoardRead,
-  TaskCustomFieldDefinitionRead,
-  TaskCustomFieldDefinitionUpdate,
-} from "@/api/generated/model";
+import type { TaskCustomFieldDefinitionUpdate } from "@/api/generated/model";
+import { CustomFieldForm } from "@/components/custom-fields/CustomFieldForm";
 import { DashboardPageLayout } from "@/components/templates/DashboardPageLayout";
-import { Button, buttonVariants } from "@/components/ui/button";
-import { Input } from "@/components/ui/input";
 import {
-  Select,
-  SelectContent,
-  SelectItem,
-  SelectTrigger,
-  SelectValue,
-} from "@/components/ui/select";
-import { Textarea } from "@/components/ui/textarea";
+  buildCustomFieldUpdatePayload,
+  deriveFormStateFromCustomField,
+  extractApiErrorMessage,
+  type NormalizedCustomFieldFormValues,
+} from "@/components/custom-fields/custom-field-form-utils";
 import { useOrganizationMembership } from "@/lib/use-organization-membership";
 
-type FormState = {
-  fieldKey: string;
-  label: string;
-  fieldType:
-    | "text"
-    | "text_long"
-    | "integer"
-    | "decimal"
-    | "boolean"
-    | "date"
-    | "date_time"
-    | "url"
-    | "json";
-  uiVisibility: "always" | "if_set" | "hidden";
-  validationRegex: string;
-  description: string;
-  required: boolean;
-  defaultValue: string;
-};
-
-type EditCustomFieldFormProps = {
-  field: TaskCustomFieldDefinitionRead;
-  boards: BoardRead[];
-  boardsLoading: boolean;
-  boardsError: string | null;
-  saving: boolean;
-  onSubmit: (updates: TaskCustomFieldDefinitionUpdate) => Promise<void>;
-};
-
-const STRING_FIELD_TYPES = new Set([
-  "text",
-  "text_long",
-  "date",
-  "date_time",
-  "url",
-]);
-
-const parseDefaultValue = (
-  fieldType: FormState["fieldType"],
-  value: string,
-): { value: unknown | null; error: string | null } => {
-  const trimmed = value.trim();
-  if (!trimmed) return { value: null, error: null };
-  if (fieldType === "text" || fieldType === "text_long") {
-    return { value: trimmed, error: null };
-  }
-  if (fieldType === "integer") {
-    if (!/^-?\d+$/.test(trimmed)) {
-      return { value: null, error: "Default value must be a valid integer." };
-    }
-    return { value: Number.parseInt(trimmed, 10), error: null };
-  }
-  if (fieldType === "decimal") {
-    if (!/^-?\d+(\.\d+)?$/.test(trimmed)) {
-      return { value: null, error: "Default value must be a valid decimal." };
-    }
-    return { value: Number.parseFloat(trimmed), error: null };
-  }
-  if (fieldType === "boolean") {
-    if (trimmed.toLowerCase() === "true") return { value: true, error: null };
-    if (trimmed.toLowerCase() === "false") return { value: false, error: null };
-    return { value: null, error: "Default value must be true or false." };
-  }
-  if (
-    fieldType === "date" ||
-    fieldType === "date_time" ||
-    fieldType === "url"
-  ) {
-    return { value: trimmed, error: null };
-  }
-  if (fieldType === "json") {
-    try {
-      const parsed = JSON.parse(trimmed);
-      if (
-        parsed === null ||
-        typeof parsed !== "object" ||
-        (!Array.isArray(parsed) && typeof parsed !== "object")
-      ) {
-        return {
-          value: null,
-          error: "Default value must be valid JSON (object or array).",
-        };
-      }
-      return { value: parsed, error: null };
-    } catch {
-      return {
-        value: null,
-        error: "Default value must be valid JSON (object or array).",
-      };
-    }
-  }
-  try {
-    return { value: JSON.parse(trimmed), error: null };
-  } catch {
-    return { value: trimmed, error: null };
-  }
-};
-
-const formatDefaultValue = (value: unknown): string => {
-  if (value === null || value === undefined) return "";
-  if (typeof value === "string") return value;
-  try {
-    return JSON.stringify(value, null, 2);
-  } catch {
-    return String(value);
-  }
-};
-
-const canonicalJson = (value: unknown): string =>
-  JSON.stringify(value) ?? "undefined";
-
-const extractErrorMessage = (error: unknown, fallback: string) => {
-  if (error instanceof ApiError) return error.message || fallback;
-  if (error instanceof Error) return error.message || fallback;
-  return fallback;
-};
-
-function EditCustomFieldForm({
-  field,
-  boards,
-  boardsLoading,
-  boardsError,
-  saving,
-  onSubmit,
-}: EditCustomFieldFormProps) {
-  const [formState, setFormState] = useState<FormState>(() => ({
-    fieldKey: field.field_key,
-    label: field.label ?? field.field_key,
-    fieldType: field.field_type ?? "text",
-    uiVisibility: field.ui_visibility ?? "always",
-    validationRegex: field.validation_regex ?? "",
-    description: field.description ?? "",
-    required: field.required === true,
-    defaultValue: formatDefaultValue(field.default_value),
-  }));
-  const [boardSearch, setBoardSearch] = useState("");
-  const [selectedBoardIds, setSelectedBoardIds] = useState<Set<string>>(
-    () => new Set(field.board_ids ?? []),
-  );
-  const [saveError, setSaveError] = useState<string | null>(null);
-
-  const filteredBoards = useMemo(() => {
-    const query = boardSearch.trim().toLowerCase();
-    if (!query) return boards;
-    return boards.filter(
-      (board) =>
-        board.name.toLowerCase().includes(query) ||
-        board.slug.toLowerCase().includes(query),
-    );
-  }, [boardSearch, boards]);
-
-  const handleSubmit = async (event: FormEvent<HTMLFormElement>) => {
-    event.preventDefault();
-    setSaveError(null);
-
-    const trimmedLabel = formState.label.trim();
-    const trimmedValidationRegex = formState.validationRegex.trim();
-    if (!trimmedLabel) {
-      setSaveError("Label is required.");
-      return;
-    }
-    if (selectedBoardIds.size === 0) {
-      setSaveError("Select at least one board.");
-      return;
-    }
-    if (
-      trimmedValidationRegex &&
-      !STRING_FIELD_TYPES.has(formState.fieldType)
-    ) {
-      setSaveError(
-        "Validation regex is only supported for string field types.",
-      );
-      return;
-    }
-    const parsedDefaultValue = parseDefaultValue(
-      formState.fieldType,
-      formState.defaultValue,
-    );
-    if (parsedDefaultValue.error) {
-      setSaveError(parsedDefaultValue.error);
-      return;
-    }
-
-    const payload = {
-      label: trimmedLabel,
-      field_type: formState.fieldType,
-      ui_visibility: formState.uiVisibility,
-      validation_regex: trimmedValidationRegex || null,
-      description: formState.description.trim() || null,
-      required: formState.required,
-      default_value: parsedDefaultValue.value,
-      board_ids: Array.from(selectedBoardIds),
-    };
-
-    const updates: TaskCustomFieldDefinitionUpdate = {};
-    if (payload.label !== (field.label ?? field.field_key)) {
-      updates.label = payload.label;
-    }
-    if (payload.field_type !== (field.field_type ?? "text")) {
-      updates.field_type = payload.field_type;
-    }
-    if (payload.ui_visibility !== (field.ui_visibility ?? "always")) {
-      updates.ui_visibility = payload.ui_visibility;
-    }
-    if (payload.validation_regex !== (field.validation_regex ?? null)) {
-      updates.validation_regex = payload.validation_regex;
-    }
-    if (payload.description !== (field.description ?? null)) {
-      updates.description = payload.description;
-    }
-    if (payload.required !== (field.required === true)) {
-      updates.required = payload.required;
-    }
-    if (
-      canonicalJson(payload.default_value) !==
-      canonicalJson(field.default_value)
-    ) {
-      updates.default_value = payload.default_value;
-    }
-    const currentBoardIds = [...(field.board_ids ?? [])].sort();
-    const nextBoardIds = [...payload.board_ids].sort();
-    if (JSON.stringify(currentBoardIds) !== JSON.stringify(nextBoardIds)) {
-      updates.board_ids = payload.board_ids;
-    }
-    if (Object.keys(updates).length === 0) {
-      setSaveError("No changes were made.");
-      return;
-    }
-
-    try {
-      await onSubmit(updates);
-    } catch (error) {
-      setSaveError(
-        extractErrorMessage(error, "Failed to update custom field."),
-      );
-    }
-  };
-
-  return (
-    <form
-      onSubmit={handleSubmit}
-      className="max-w-3xl rounded-xl border border-slate-200 bg-white p-6 shadow-sm space-y-6"
-    >
-      <div>
-        <p className="text-xs font-semibold uppercase tracking-wider text-slate-500">
-          Basic configuration
-        </p>
-        <div className="mt-4 grid gap-6 md:grid-cols-2">
-          <label className="space-y-1">
-            <span className="text-sm font-semibold text-slate-900">
-              Field key
-            </span>
-            <Input
-              value={formState.fieldKey}
-              placeholder="e.g. client_name"
-              readOnly
-              disabled
-            />
-            <span className="text-xs text-slate-500">
-              Field key cannot be changed after creation.
-            </span>
-          </label>
-          <label className="space-y-1">
-            <span className="text-sm font-semibold text-slate-900">Label</span>
-            <Input
-              value={formState.label}
-              onChange={(event) =>
-                setFormState((prev) => ({ ...prev, label: event.target.value }))
-              }
-              placeholder="e.g. Client name"
-              disabled={saving}
-              required
-            />
-          </label>
-          <label className="space-y-1">
-            <span className="text-sm font-semibold text-slate-900">
-              Field type
-            </span>
-            <Select
-              value={formState.fieldType}
-              onValueChange={(value) =>
-                setFormState((prev) => ({
-                  ...prev,
-                  fieldType: value as FormState["fieldType"],
-                }))
-              }
-              disabled={saving}
-            >
-              <SelectTrigger>
-                <SelectValue placeholder="Select field type" />
-              </SelectTrigger>
-              <SelectContent>
-                <SelectItem value="text">Text</SelectItem>
-                <SelectItem value="text_long">Text (long)</SelectItem>
-                <SelectItem value="integer">Integer</SelectItem>
-                <SelectItem value="decimal">Decimal</SelectItem>
-                <SelectItem value="boolean">Boolean (true/false)</SelectItem>
-                <SelectItem value="date">Date</SelectItem>
-                <SelectItem value="date_time">Date &amp; time</SelectItem>
-                <SelectItem value="url">URL</SelectItem>
-                <SelectItem value="json">JSON</SelectItem>
-              </SelectContent>
-            </Select>
-          </label>
-          <label className="space-y-1">
-            <span className="text-sm font-semibold text-slate-900">
-              UI visible
-            </span>
-            <Select
-              value={formState.uiVisibility}
-              onValueChange={(value) =>
-                setFormState((prev) => ({
-                  ...prev,
-                  uiVisibility: value as FormState["uiVisibility"],
-                }))
-              }
-              disabled={saving}
-            >
-              <SelectTrigger>
-                <SelectValue placeholder="Select visibility" />
-              </SelectTrigger>
-              <SelectContent>
-                <SelectItem value="always">Always</SelectItem>
-                <SelectItem value="if_set">If set</SelectItem>
-                <SelectItem value="hidden">Hidden</SelectItem>
-              </SelectContent>
-            </Select>
-          </label>
-        </div>
-        <label className="mt-4 flex items-center gap-2 text-sm text-slate-700">
-          <input
-            type="checkbox"
-            checked={formState.required}
-            onChange={(event) =>
-              setFormState((prev) => ({
-                ...prev,
-                required: event.target.checked,
-              }))
-            }
-            disabled={saving}
-          />
-          Required
-        </label>
-      </div>
-
-      <div>
-        <p className="text-xs font-semibold uppercase tracking-wider text-slate-500">
-          Validation and defaults
-        </p>
-        <div className="mt-4 space-y-4">
-          <label className="space-y-1">
-            <span className="text-sm font-semibold text-slate-900">
-              Validation regex
-            </span>
-            <Input
-              value={formState.validationRegex}
-              onChange={(event) =>
-                setFormState((prev) => ({
-                  ...prev,
-                  validationRegex: event.target.value,
-                }))
-              }
-              placeholder="Optional. Example: ^[A-Z]{3}$"
-              disabled={saving || !STRING_FIELD_TYPES.has(formState.fieldType)}
-            />
-            <p className="text-xs text-slate-500">
-              Supported for text/date/date-time/url fields.
-            </p>
-          </label>
-          <label className="space-y-1">
-            <span className="text-sm font-semibold text-slate-900">
-              Default value
-            </span>
-            <Textarea
-              value={formState.defaultValue}
-              onChange={(event) =>
-                setFormState((prev) => ({
-                  ...prev,
-                  defaultValue: event.target.value,
-                }))
-              }
-              rows={3}
-              placeholder='Optional default value. For booleans use "true"/"false"; for JSON use an object or array.'
-              disabled={saving}
-            />
-          </label>
-          <label className="space-y-1">
-            <span className="text-sm font-semibold text-slate-900">
-              Description
-            </span>
-            <Textarea
-              value={formState.description}
-              onChange={(event) =>
-                setFormState((prev) => ({
-                  ...prev,
-                  description: event.target.value,
-                }))
-              }
-              rows={3}
-              placeholder="Optional description used by agents and UI"
-              disabled={saving}
-            />
-          </label>
-        </div>
-      </div>
-
-      <div>
-        <div className="flex flex-wrap items-center justify-between gap-2">
-          <p className="text-xs font-semibold uppercase tracking-wider text-slate-500">
-            Board bindings
-          </p>
-          <span className="text-xs text-slate-500">
-            {selectedBoardIds.size} selected
-          </span>
-        </div>
-        <div className="mt-4 space-y-2">
-          <Input
-            value={boardSearch}
-            onChange={(event) => setBoardSearch(event.target.value)}
-            placeholder="Search boards..."
-            disabled={saving}
-          />
-          <div className="max-h-64 overflow-auto rounded-xl border border-slate-200 bg-slate-50/40">
-            {boardsLoading ? (
-              <div className="px-4 py-6 text-sm text-slate-500">
-                Loading boards…
-              </div>
-            ) : boardsError ? (
-              <div className="px-4 py-6 text-sm text-rose-700">
-                {boardsError}
-              </div>
-            ) : filteredBoards.length === 0 ? (
-              <div className="px-4 py-6 text-sm text-slate-500">
-                No boards found.
-              </div>
-            ) : (
-              <ul className="divide-y divide-slate-200">
-                {filteredBoards.map((board) => {
-                  const checked = selectedBoardIds.has(board.id);
-                  return (
-                    <li key={board.id} className="px-4 py-3">
-                      <label className="flex cursor-pointer items-start gap-3">
-                        <input
-                          type="checkbox"
-                          className="mt-1 h-4 w-4 rounded border-slate-300 text-blue-600"
-                          checked={checked}
-                          onChange={() => {
-                            setSelectedBoardIds((prev) => {
-                              const next = new Set(prev);
-                              if (next.has(board.id)) {
-                                next.delete(board.id);
-                              } else {
-                                next.add(board.id);
-                              }
-                              return next;
-                            });
-                          }}
-                          disabled={saving}
-                        />
-                        <div className="min-w-0">
-                          <p className="truncate text-sm font-medium text-slate-900">
-                            {board.name}
-                          </p>
-                          <p className="mt-1 text-xs text-slate-500">
-                            {board.slug}
-                          </p>
-                        </div>
-                      </label>
-                    </li>
-                  );
-                })}
-              </ul>
-            )}
-          </div>
-          <p className="text-xs text-slate-500">
-            Required. The custom field appears on tasks in selected boards.
-          </p>
-        </div>
-      </div>
-
-      {saveError ? <p className="text-sm text-rose-600">{saveError}</p> : null}
-      <div className="flex items-center gap-2">
-        <Link
-          href="/custom-fields"
-          className={buttonVariants({ variant: "outline" })}
-          aria-disabled={saving}
-        >
-          Cancel
-        </Link>
-        <Button type="submit" disabled={saving}>
-          {saving ? "Saving..." : "Save changes"}
-        </Button>
-      </div>
-    </form>
-  );
-}
-
 export default function EditCustomFieldPage() {
   const router = useRouter();
   const params = useParams();
@@ -555,6 +50,7 @@ export default function EditCustomFieldPage() {
         refetchOnMount: "always",
       },
     });
+
   const field = useMemo(() => {
     if (!fieldId || customFieldsQuery.data?.status !== 200) return null;
     return (
@@ -575,6 +71,7 @@ export default function EditCustomFieldPage() {
       },
     },
   );
+
   const boards = useMemo(
     () =>
       boardsQuery.data?.status === 200
@@ -585,14 +82,13 @@ export default function EditCustomFieldPage() {
 
   const updateMutation =
     useUpdateOrgCustomFieldApiV1OrganizationsMeCustomFieldsTaskCustomFieldDefinitionIdPatch<ApiError>();
-  const saving = updateMutation.isPending;
   const customFieldsKey =
     getListOrgCustomFieldsApiV1OrganizationsMeCustomFieldsGetQueryKey();
 
   const loadError = useMemo(() => {
     if (!fieldId) return "Missing custom field id.";
     if (customFieldsQuery.error) {
-      return extractErrorMessage(
+      return extractApiErrorMessage(
         customFieldsQuery.error,
         "Failed to load custom field.",
       );
@@ -602,8 +98,15 @@ export default function EditCustomFieldPage() {
     return null;
   }, [customFieldsQuery.error, customFieldsQuery.isLoading, field, fieldId]);
 
-  const handleSubmit = async (updates: TaskCustomFieldDefinitionUpdate) => {
-    if (!fieldId) return;
+  const handleSubmit = async (values: NormalizedCustomFieldFormValues) => {
+    if (!fieldId || !field) return;
+
+    const updates: TaskCustomFieldDefinitionUpdate =
+      buildCustomFieldUpdatePayload(field, values);
+    if (Object.keys(updates).length === 0) {
+      throw new Error("No changes were made.");
+    }
+
     await updateMutation.mutateAsync({
       taskCustomFieldDefinitionId: fieldId,
       data: updates,
@@ -636,13 +139,18 @@ export default function EditCustomFieldPage() {
         </div>
       ) : null}
       {!customFieldsQuery.isLoading && !loadError && field ? (
-        <EditCustomFieldForm
+        <CustomFieldForm
           key={field.id}
-          field={field}
+          mode="edit"
+          initialFormState={deriveFormStateFromCustomField(field)}
+          initialBoardIds={field.board_ids ?? []}
           boards={boards}
           boardsLoading={boardsQuery.isLoading}
           boardsError={boardsQuery.error?.message ?? null}
-          saving={saving}
+          isSubmitting={updateMutation.isPending}
+          submitLabel="Save changes"
+          submittingLabel="Saving..."
+          submitErrorFallback="Failed to update custom field."
           onSubmit={handleSubmit}
         />
       ) : null}
diff --git a/frontend/src/app/custom-fields/new/page.tsx b/frontend/src/app/custom-fields/new/page.tsx
index 095e1a16..52450ae1 100644
--- a/frontend/src/app/custom-fields/new/page.tsx
+++ b/frontend/src/app/custom-fields/new/page.tsx
@@ -2,8 +2,7 @@
 
 export const dynamic = "force-dynamic";
 
-import { type FormEvent, useMemo, useState } from "react";
-import Link from "next/link";
+import { useMemo } from "react";
 import { useRouter } from "next/navigation";
 
 import { useAuth } from "@/auth/clerk";
@@ -18,139 +17,21 @@ import {
   getListOrgCustomFieldsApiV1OrganizationsMeCustomFieldsGetQueryKey,
   useCreateOrgCustomFieldApiV1OrganizationsMeCustomFieldsPost,
 } from "@/api/generated/org-custom-fields/org-custom-fields";
-import type { TaskCustomFieldDefinitionCreate } from "@/api/generated/model";
-import { DashboardPageLayout } from "@/components/templates/DashboardPageLayout";
-import { Button, buttonVariants } from "@/components/ui/button";
-import { Input } from "@/components/ui/input";
+import { CustomFieldForm } from "@/components/custom-fields/CustomFieldForm";
+import { DEFAULT_CUSTOM_FIELD_FORM_STATE } from "@/components/custom-fields/custom-field-form-types";
 import {
-  Select,
-  SelectContent,
-  SelectItem,
-  SelectTrigger,
-  SelectValue,
-} from "@/components/ui/select";
-import { Textarea } from "@/components/ui/textarea";
+  createCustomFieldPayload,
+  type NormalizedCustomFieldFormValues,
+} from "@/components/custom-fields/custom-field-form-utils";
+import { DashboardPageLayout } from "@/components/templates/DashboardPageLayout";
 import { useOrganizationMembership } from "@/lib/use-organization-membership";
 
-type FormState = {
-  fieldKey: string;
-  label: string;
-  fieldType:
-    | "text"
-    | "text_long"
-    | "integer"
-    | "decimal"
-    | "boolean"
-    | "date"
-    | "date_time"
-    | "url"
-    | "json";
-  uiVisibility: "always" | "if_set" | "hidden";
-  validationRegex: string;
-  description: string;
-  required: boolean;
-  defaultValue: string;
-};
-
-const defaultFormState: FormState = {
-  fieldKey: "",
-  label: "",
-  fieldType: "text",
-  uiVisibility: "always",
-  validationRegex: "",
-  description: "",
-  required: false,
-  defaultValue: "",
-};
-
-const STRING_FIELD_TYPES = new Set([
-  "text",
-  "text_long",
-  "date",
-  "date_time",
-  "url",
-]);
-
-const parseDefaultValue = (
-  fieldType: FormState["fieldType"],
-  value: string,
-): { value: unknown | null; error: string | null } => {
-  const trimmed = value.trim();
-  if (!trimmed) return { value: null, error: null };
-  if (fieldType === "text" || fieldType === "text_long") {
-    return { value: trimmed, error: null };
-  }
-  if (fieldType === "integer") {
-    if (!/^-?\d+$/.test(trimmed)) {
-      return { value: null, error: "Default value must be a valid integer." };
-    }
-    return { value: Number.parseInt(trimmed, 10), error: null };
-  }
-  if (fieldType === "decimal") {
-    if (!/^-?\d+(\.\d+)?$/.test(trimmed)) {
-      return { value: null, error: "Default value must be a valid decimal." };
-    }
-    return { value: Number.parseFloat(trimmed), error: null };
-  }
-  if (fieldType === "boolean") {
-    if (trimmed.toLowerCase() === "true") return { value: true, error: null };
-    if (trimmed.toLowerCase() === "false") return { value: false, error: null };
-    return { value: null, error: "Default value must be true or false." };
-  }
-  if (
-    fieldType === "date" ||
-    fieldType === "date_time" ||
-    fieldType === "url"
-  ) {
-    return { value: trimmed, error: null };
-  }
-  if (fieldType === "json") {
-    try {
-      const parsed = JSON.parse(trimmed);
-      if (
-        parsed === null ||
-        typeof parsed !== "object" ||
-        (!Array.isArray(parsed) && typeof parsed !== "object")
-      ) {
-        return {
-          value: null,
-          error: "Default value must be valid JSON (object or array).",
-        };
-      }
-      return { value: parsed, error: null };
-    } catch {
-      return {
-        value: null,
-        error: "Default value must be valid JSON (object or array).",
-      };
-    }
-  }
-  try {
-    return { value: JSON.parse(trimmed), error: null };
-  } catch {
-    return { value: trimmed, error: null };
-  }
-};
-
-const extractErrorMessage = (error: unknown, fallback: string) => {
-  if (error instanceof ApiError) return error.message || fallback;
-  if (error instanceof Error) return error.message || fallback;
-  return fallback;
-};
-
 export default function NewCustomFieldPage() {
   const router = useRouter();
   const { isSignedIn } = useAuth();
   const { isAdmin } = useOrganizationMembership(isSignedIn);
   const queryClient = useQueryClient();
 
-  const [formState, setFormState] = useState<FormState>(defaultFormState);
-  const [boardSearch, setBoardSearch] = useState("");
-  const [selectedBoardIds, setSelectedBoardIds] = useState<Set<string>>(
-    () => new Set(),
-  );
-  const [error, setError] = useState<string | null>(null);
-
   const boardsQuery = useListBoardsApiV1BoardsGet<
     listBoardsApiV1BoardsGetResponse,
     ApiError
@@ -164,6 +45,7 @@ export default function NewCustomFieldPage() {
       },
     },
   );
+
   const boards = useMemo(
     () =>
       boardsQuery.data?.status === 200
@@ -171,79 +53,18 @@ export default function NewCustomFieldPage() {
         : [],
     [boardsQuery.data],
   );
-  const filteredBoards = useMemo(() => {
-    const query = boardSearch.trim().toLowerCase();
-    if (!query) return boards;
-    return boards.filter(
-      (board) =>
-        board.name.toLowerCase().includes(query) ||
-        board.slug.toLowerCase().includes(query),
-    );
-  }, [boardSearch, boards]);
 
   const createMutation =
     useCreateOrgCustomFieldApiV1OrganizationsMeCustomFieldsPost<ApiError>();
-  const saving = createMutation.isPending;
   const customFieldsKey =
     getListOrgCustomFieldsApiV1OrganizationsMeCustomFieldsGetQueryKey();
 
-  const handleSubmit = async (event: FormEvent<HTMLFormElement>) => {
-    event.preventDefault();
-    if (!isSignedIn || saving) return;
-    setError(null);
-
-    const trimmedFieldKey = formState.fieldKey.trim();
-    const trimmedLabel = formState.label.trim();
-    const trimmedValidationRegex = formState.validationRegex.trim();
-    if (!trimmedFieldKey) {
-      setError("Field key is required.");
-      return;
-    }
-    if (!trimmedLabel) {
-      setError("Label is required.");
-      return;
-    }
-    if (selectedBoardIds.size === 0) {
-      setError("Select at least one board.");
-      return;
-    }
-    if (
-      trimmedValidationRegex &&
-      !STRING_FIELD_TYPES.has(formState.fieldType)
-    ) {
-      setError("Validation regex is only supported for string field types.");
-      return;
-    }
-    const parsedDefaultValue = parseDefaultValue(
-      formState.fieldType,
-      formState.defaultValue,
-    );
-    if (parsedDefaultValue.error) {
-      setError(parsedDefaultValue.error);
-      return;
-    }
-
-    const payload: TaskCustomFieldDefinitionCreate = {
-      field_key: trimmedFieldKey,
-      label: trimmedLabel,
-      field_type: formState.fieldType,
-      ui_visibility: formState.uiVisibility,
-      validation_regex: trimmedValidationRegex || null,
-      description: formState.description.trim() || null,
-      required: formState.required,
-      default_value: parsedDefaultValue.value,
-      board_ids: Array.from(selectedBoardIds),
-    };
-
-    try {
-      await createMutation.mutateAsync({ data: payload });
-      await queryClient.invalidateQueries({ queryKey: customFieldsKey });
-      router.push("/custom-fields");
-    } catch (submitError) {
-      setError(
-        extractErrorMessage(submitError, "Failed to create custom field."),
-      );
-    }
+  const handleSubmit = async (values: NormalizedCustomFieldFormValues) => {
+    await createMutation.mutateAsync({
+      data: createCustomFieldPayload(values),
+    });
+    await queryClient.invalidateQueries({ queryKey: customFieldsKey });
+    router.push("/custom-fields");
   };
 
   return (
@@ -259,271 +80,18 @@ export default function NewCustomFieldPage() {
       adminOnlyMessage="Only organization owners and admins can manage custom fields."
       stickyHeader
     >
-      <form
+      <CustomFieldForm
+        mode="create"
+        initialFormState={DEFAULT_CUSTOM_FIELD_FORM_STATE}
+        boards={boards}
+        boardsLoading={boardsQuery.isLoading}
+        boardsError={boardsQuery.error?.message ?? null}
+        isSubmitting={createMutation.isPending}
+        submitLabel="Create field"
+        submittingLabel="Creating..."
+        submitErrorFallback="Failed to create custom field."
         onSubmit={handleSubmit}
-        className="max-w-3xl rounded-xl border border-slate-200 bg-white p-6 shadow-sm space-y-6"
-      >
-        <div>
-          <p className="text-xs font-semibold uppercase tracking-wider text-slate-500">
-            Basic configuration
-          </p>
-          <div className="mt-4 grid gap-6 md:grid-cols-2">
-            <label className="space-y-1">
-              <span className="text-sm font-semibold text-slate-900">
-                Field key
-              </span>
-              <Input
-                value={formState.fieldKey}
-                onChange={(event) =>
-                  setFormState((prev) => ({
-                    ...prev,
-                    fieldKey: event.target.value,
-                  }))
-                }
-                placeholder="e.g. client_name"
-                disabled={saving}
-                required
-              />
-            </label>
-            <label className="space-y-1">
-              <span className="text-sm font-semibold text-slate-900">
-                Label
-              </span>
-              <Input
-                value={formState.label}
-                onChange={(event) =>
-                  setFormState((prev) => ({
-                    ...prev,
-                    label: event.target.value,
-                  }))
-                }
-                placeholder="e.g. Client name"
-                disabled={saving}
-                required
-              />
-            </label>
-            <label className="space-y-1">
-              <span className="text-sm font-semibold text-slate-900">
-                Field type
-              </span>
-              <Select
-                value={formState.fieldType}
-                onValueChange={(value) =>
-                  setFormState((prev) => ({
-                    ...prev,
-                    fieldType: value as FormState["fieldType"],
-                  }))
-                }
-                disabled={saving}
-              >
-                <SelectTrigger>
-                  <SelectValue placeholder="Select field type" />
-                </SelectTrigger>
-                <SelectContent>
-                  <SelectItem value="text">Text</SelectItem>
-                  <SelectItem value="text_long">Text (long)</SelectItem>
-                  <SelectItem value="integer">Integer</SelectItem>
-                  <SelectItem value="decimal">Decimal</SelectItem>
-                  <SelectItem value="boolean">Boolean (true/false)</SelectItem>
-                  <SelectItem value="date">Date</SelectItem>
-                  <SelectItem value="date_time">Date &amp; time</SelectItem>
-                  <SelectItem value="url">URL</SelectItem>
-                  <SelectItem value="json">JSON</SelectItem>
-                </SelectContent>
-              </Select>
-            </label>
-            <label className="space-y-1">
-              <span className="text-sm font-semibold text-slate-900">
-                UI visible
-              </span>
-              <Select
-                value={formState.uiVisibility}
-                onValueChange={(value) =>
-                  setFormState((prev) => ({
-                    ...prev,
-                    uiVisibility: value as FormState["uiVisibility"],
-                  }))
-                }
-                disabled={saving}
-              >
-                <SelectTrigger>
-                  <SelectValue placeholder="Select visibility" />
-                </SelectTrigger>
-                <SelectContent>
-                  <SelectItem value="always">Always</SelectItem>
-                  <SelectItem value="if_set">If set</SelectItem>
-                  <SelectItem value="hidden">Hidden</SelectItem>
-                </SelectContent>
-              </Select>
-            </label>
-          </div>
-          <label className="mt-4 flex items-center gap-2 text-sm text-slate-700">
-            <input
-              type="checkbox"
-              checked={formState.required}
-              onChange={(event) =>
-                setFormState((prev) => ({
-                  ...prev,
-                  required: event.target.checked,
-                }))
-              }
-              disabled={saving}
-            />
-            Required
-          </label>
-        </div>
-
-        <div>
-          <p className="text-xs font-semibold uppercase tracking-wider text-slate-500">
-            Validation and defaults
-          </p>
-          <div className="mt-4 space-y-4">
-            <label className="space-y-1">
-              <span className="text-sm font-semibold text-slate-900">
-                Validation regex
-              </span>
-              <Input
-                value={formState.validationRegex}
-                onChange={(event) =>
-                  setFormState((prev) => ({
-                    ...prev,
-                    validationRegex: event.target.value,
-                  }))
-                }
-                placeholder="Optional. Example: ^[A-Z]{3}$"
-                disabled={
-                  saving || !STRING_FIELD_TYPES.has(formState.fieldType)
-                }
-              />
-              <p className="text-xs text-slate-500">
-                Supported for text/date/date-time/url fields.
-              </p>
-            </label>
-            <label className="space-y-1">
-              <span className="text-sm font-semibold text-slate-900">
-                Default value
-              </span>
-              <Textarea
-                value={formState.defaultValue}
-                onChange={(event) =>
-                  setFormState((prev) => ({
-                    ...prev,
-                    defaultValue: event.target.value,
-                  }))
-                }
-                rows={3}
-                placeholder='Optional default value. For booleans use "true"/"false"; for JSON use an object or array.'
-                disabled={saving}
-              />
-            </label>
-            <label className="space-y-1">
-              <span className="text-sm font-semibold text-slate-900">
-                Description
-              </span>
-              <Textarea
-                value={formState.description}
-                onChange={(event) =>
-                  setFormState((prev) => ({
-                    ...prev,
-                    description: event.target.value,
-                  }))
-                }
-                rows={3}
-                placeholder="Optional description used by agents and UI"
-                disabled={saving}
-              />
-            </label>
-          </div>
-        </div>
-
-        <div>
-          <div className="flex flex-wrap items-center justify-between gap-2">
-            <p className="text-xs font-semibold uppercase tracking-wider text-slate-500">
-              Board bindings
-            </p>
-            <span className="text-xs text-slate-500">
-              {selectedBoardIds.size} selected
-            </span>
-          </div>
-          <div className="mt-4 space-y-2">
-            <Input
-              value={boardSearch}
-              onChange={(event) => setBoardSearch(event.target.value)}
-              placeholder="Search boards..."
-              disabled={saving}
-            />
-            <div className="max-h-64 overflow-auto rounded-xl border border-slate-200 bg-slate-50/40">
-              {boardsQuery.isLoading ? (
-                <div className="px-4 py-6 text-sm text-slate-500">
-                  Loading boards…
-                </div>
-              ) : boardsQuery.error ? (
-                <div className="px-4 py-6 text-sm text-rose-700">
-                  {boardsQuery.error.message}
-                </div>
-              ) : filteredBoards.length === 0 ? (
-                <div className="px-4 py-6 text-sm text-slate-500">
-                  No boards found.
-                </div>
-              ) : (
-                <ul className="divide-y divide-slate-200">
-                  {filteredBoards.map((board) => {
-                    const checked = selectedBoardIds.has(board.id);
-                    return (
-                      <li key={board.id} className="px-4 py-3">
-                        <label className="flex cursor-pointer items-start gap-3">
-                          <input
-                            type="checkbox"
-                            className="mt-1 h-4 w-4 rounded border-slate-300 text-blue-600"
-                            checked={checked}
-                            onChange={() => {
-                              setSelectedBoardIds((prev) => {
-                                const next = new Set(prev);
-                                if (next.has(board.id)) {
-                                  next.delete(board.id);
-                                } else {
-                                  next.add(board.id);
-                                }
-                                return next;
-                              });
-                            }}
-                            disabled={saving}
-                          />
-                          <div className="min-w-0">
-                            <p className="truncate text-sm font-medium text-slate-900">
-                              {board.name}
-                            </p>
-                            <p className="mt-1 text-xs text-slate-500">
-                              {board.slug}
-                            </p>
-                          </div>
-                        </label>
-                      </li>
-                    );
-                  })}
-                </ul>
-              )}
-            </div>
-            <p className="text-xs text-slate-500">
-              Required. The custom field appears on tasks in selected boards.
-            </p>
-          </div>
-        </div>
-
-        {error ? <p className="text-sm text-rose-600">{error}</p> : null}
-        <div className="flex items-center gap-2">
-          <Link
-            href="/custom-fields"
-            className={buttonVariants({ variant: "outline" })}
-            aria-disabled={saving}
-          >
-            Cancel
-          </Link>
-          <Button type="submit" disabled={saving}>
-            {saving ? "Creating..." : "Create field"}
-          </Button>
-        </div>
-      </form>
+      />
     </DashboardPageLayout>
   );
 }
diff --git a/frontend/src/app/custom-fields/page.tsx b/frontend/src/app/custom-fields/page.tsx
index ad2d8d4c..b3a96f5d 100644
--- a/frontend/src/app/custom-fields/page.tsx
+++ b/frontend/src/app/custom-fields/page.tsx
@@ -17,6 +17,7 @@ import {
 } from "@/api/generated/org-custom-fields/org-custom-fields";
 import type { TaskCustomFieldDefinitionRead } from "@/api/generated/model";
 import { CustomFieldsTable } from "@/components/custom-fields/CustomFieldsTable";
+import { extractApiErrorMessage } from "@/components/custom-fields/custom-field-form-utils";
 import { DashboardPageLayout } from "@/components/templates/DashboardPageLayout";
 import { buttonVariants } from "@/components/ui/button";
 import { ConfirmActionDialog } from "@/components/ui/confirm-action-dialog";
@@ -25,12 +26,6 @@ import { useUrlSorting } from "@/lib/use-url-sorting";
 
 const CUSTOM_FIELD_SORTABLE_COLUMNS = ["field_key", "required", "updated_at"];
 
-const extractErrorMessage = (error: unknown, fallback: string) => {
-  if (error instanceof ApiError) return error.message || fallback;
-  if (error instanceof Error) return error.message || fallback;
-  return fallback;
-};
-
 export default function CustomFieldsPage() {
   const { isSignedIn } = useAuth();
   const { isAdmin } = useOrganizationMembership(isSignedIn);
@@ -150,7 +145,7 @@ export default function CustomFieldsPage() {
         }
         errorMessage={
           deleteMutation.error
-            ? extractErrorMessage(
+            ? extractApiErrorMessage(
                 deleteMutation.error,
                 "Unable to delete custom field.",
               )
diff --git a/frontend/src/components/custom-fields/CustomFieldForm.test.tsx b/frontend/src/components/custom-fields/CustomFieldForm.test.tsx
new file mode 100644
index 00000000..53a861b3
--- /dev/null
+++ b/frontend/src/components/custom-fields/CustomFieldForm.test.tsx
@@ -0,0 +1,136 @@
+import type React from "react";
+import { fireEvent, render, screen, waitFor } from "@testing-library/react";
+import { describe, expect, it, vi } from "vitest";
+
+import type { BoardRead } from "@/api/generated/model";
+import { CustomFieldForm } from "./CustomFieldForm";
+import { DEFAULT_CUSTOM_FIELD_FORM_STATE } from "./custom-field-form-types";
+
+vi.mock("next/link", () => {
+  type LinkProps = React.PropsWithChildren<{
+    href: string | { pathname?: string };
+  }> &
+    Omit<React.AnchorHTMLAttributes<HTMLAnchorElement>, "href">;
+
+  return {
+    default: ({ href, children, ...props }: LinkProps) => (
+      <a href={typeof href === "string" ? href : "#"} {...props}>
+        {children}
+      </a>
+    ),
+  };
+});
+
+const buildBoard = (overrides: Partial<BoardRead> = {}): BoardRead => ({
+  id: "board-1",
+  name: "Operations",
+  slug: "operations",
+  description: "Operations board",
+  organization_id: "org-1",
+  created_at: "2026-01-01T00:00:00Z",
+  updated_at: "2026-01-01T00:00:00Z",
+  ...overrides,
+});
+
+describe("CustomFieldForm", () => {
+  it("validates board selection on create", async () => {
+    const onSubmit = vi.fn().mockResolvedValue(undefined);
+    render(
+      <CustomFieldForm
+        mode="create"
+        initialFormState={DEFAULT_CUSTOM_FIELD_FORM_STATE}
+        boards={[buildBoard()]}
+        boardsLoading={false}
+        boardsError={null}
+        isSubmitting={false}
+        submitLabel="Create field"
+        submittingLabel="Creating..."
+        submitErrorFallback="Failed to create custom field."
+        onSubmit={onSubmit}
+      />,
+    );
+
+    fireEvent.change(screen.getByLabelText("Field key"), {
+      target: { value: "client_name" },
+    });
+    fireEvent.change(screen.getByLabelText("Label"), {
+      target: { value: "Client Name" },
+    });
+    fireEvent.click(screen.getByRole("button", { name: "Create field" }));
+
+    await waitFor(() => {
+      expect(
+        screen.getByText("Select at least one board."),
+      ).toBeInTheDocument();
+    });
+    expect(onSubmit).not.toHaveBeenCalled();
+  });
+
+  it("submits normalized values on create", async () => {
+    const onSubmit = vi.fn().mockResolvedValue(undefined);
+    render(
+      <CustomFieldForm
+        mode="create"
+        initialFormState={DEFAULT_CUSTOM_FIELD_FORM_STATE}
+        boards={[buildBoard()]}
+        boardsLoading={false}
+        boardsError={null}
+        isSubmitting={false}
+        submitLabel="Create field"
+        submittingLabel="Creating..."
+        submitErrorFallback="Failed to create custom field."
+        onSubmit={onSubmit}
+      />,
+    );
+
+    fireEvent.change(screen.getByLabelText("Field key"), {
+      target: { value: "  client_name " },
+    });
+    fireEvent.change(screen.getByLabelText("Label"), {
+      target: { value: " Client Name " },
+    });
+    fireEvent.click(screen.getByRole("checkbox", { name: /operations/i }));
+    fireEvent.click(screen.getByRole("button", { name: "Create field" }));
+
+    await waitFor(() => {
+      expect(onSubmit).toHaveBeenCalledWith({
+        fieldKey: "client_name",
+        label: "Client Name",
+        fieldType: "text",
+        uiVisibility: "always",
+        validationRegex: null,
+        description: null,
+        required: false,
+        defaultValue: null,
+        boardIds: ["board-1"],
+      });
+    });
+  });
+
+  it("locks field key in edit mode", () => {
+    render(
+      <CustomFieldForm
+        mode="edit"
+        initialFormState={{
+          ...DEFAULT_CUSTOM_FIELD_FORM_STATE,
+          fieldKey: "client_name",
+          label: "Client Name",
+        }}
+        initialBoardIds={["board-1"]}
+        boards={[buildBoard()]}
+        boardsLoading={false}
+        boardsError={null}
+        isSubmitting={false}
+        submitLabel="Save changes"
+        submittingLabel="Saving..."
+        submitErrorFallback="Failed to update custom field."
+        onSubmit={vi.fn().mockResolvedValue(undefined)}
+      />,
+    );
+
+    expect(screen.getByDisplayValue("client_name")).toBeDisabled();
+    expect(
+      screen.getByText("Field key cannot be changed after creation."),
+    ).toBeInTheDocument();
+  });
+});
diff --git a/frontend/src/components/custom-fields/CustomFieldForm.tsx b/frontend/src/components/custom-fields/CustomFieldForm.tsx
new file mode 100644
index 00000000..80c4d2fc
--- /dev/null
+++ b/frontend/src/components/custom-fields/CustomFieldForm.tsx
@@ -0,0 +1,368 @@
+import { type FormEvent, useMemo, useState } from "react";
+import Link from "next/link";
+
+import type { BoardRead } from "@/api/generated/model";
+import { Button, buttonVariants } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import { Textarea } from "@/components/ui/textarea";
+
+import {
+  CUSTOM_FIELD_TYPE_OPTIONS,
+  CUSTOM_FIELD_VISIBILITY_OPTIONS,
+  type CustomFieldFormMode,
+  type CustomFieldFormState,
+  STRING_VALIDATION_FIELD_TYPES,
+} from "./custom-field-form-types";
+import {
+  extractApiErrorMessage,
+  filterBoardsBySearch,
+  normalizeCustomFieldFormInput,
+  type NormalizedCustomFieldFormValues,
+} from "./custom-field-form-utils";
+
+type CustomFieldFormProps = {
+  mode: CustomFieldFormMode;
+  initialFormState: CustomFieldFormState;
+  initialBoardIds?: string[];
+  boards: BoardRead[];
+  boardsLoading: boolean;
+  boardsError: string | null;
+  isSubmitting: boolean;
+  submitLabel: string;
+  submittingLabel: string;
+  submitErrorFallback: string;
+  cancelHref?: string;
+  onSubmit: (values: NormalizedCustomFieldFormValues) => Promise<void>;
+};
+
+export function CustomFieldForm({
+  mode,
+  initialFormState,
+  initialBoardIds = [],
+  boards,
+  boardsLoading,
+  boardsError,
+  isSubmitting,
+  submitLabel,
+  submittingLabel,
+  submitErrorFallback,
+  cancelHref = "/custom-fields",
+  onSubmit,
+}: CustomFieldFormProps) {
+  const [formState, setFormState] =
+    useState<CustomFieldFormState>(initialFormState);
+  const [boardSearch, setBoardSearch] = useState("");
+  const [selectedBoardIds, setSelectedBoardIds] = useState<Set<string>>(
+    () => new Set(initialBoardIds),
+  );
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  const filteredBoards = useMemo(
+    () => filterBoardsBySearch(boards, boardSearch),
+    [boardSearch, boards],
+  );
+
+  const handleSubmit = async (event: FormEvent<HTMLFormElement>) => {
+    event.preventDefault();
+    setSubmitError(null);
+
+    const normalized = normalizeCustomFieldFormInput({
+      mode,
+      formState,
+      selectedBoardIds,
+    });
+    if (normalized.value === null) {
+      setSubmitError(normalized.error);
+      return;
+    }
+
+    try {
+      await onSubmit(normalized.value);
+    } catch (error) {
+      setSubmitError(extractApiErrorMessage(error, submitErrorFallback));
+    }
+  };
+
+  return (
+    <form
+      onSubmit={handleSubmit}
+      className="max-w-3xl rounded-xl border border-slate-200 bg-white p-6 shadow-sm space-y-6"
+    >
+      <div>
+        <p className="text-xs font-semibold uppercase tracking-wider text-slate-500">
+          Basic configuration
+        </p>
+        <div className="mt-4 grid gap-6 md:grid-cols-2">
+          <label className="space-y-1">
+            <span className="text-sm font-semibold text-slate-900">
+              Field key
+            </span>
+            <Input
+              value={formState.fieldKey}
+              onChange={(event) =>
+                setFormState((prev) => ({
+                  ...prev,
+                  fieldKey: event.target.value,
+                }))
+              }
+              placeholder="e.g. client_name"
+              readOnly={mode === "edit"}
+              disabled={isSubmitting || mode === "edit"}
+              required={mode === "create"}
+            />
+            {mode === "edit" ? (
+              <span className="text-xs text-slate-500">
+                Field key cannot be changed after creation.
+              </span>
+            ) : null}
+          </label>
+
+          <label className="space-y-1">
+            <span className="text-sm font-semibold text-slate-900">Label</span>
+            <Input
+              value={formState.label}
+              onChange={(event) =>
+                setFormState((prev) => ({ ...prev, label: event.target.value }))
+              }
+              placeholder="e.g. Client name"
+              disabled={isSubmitting}
+              required
+            />
+          </label>
+
+          <label className="space-y-1">
+            <span className="text-sm font-semibold text-slate-900">
+              Field type
+            </span>
+            <Select
+              value={formState.fieldType}
+              onValueChange={(value) =>
+                setFormState((prev) => ({
+                  ...prev,
+                  fieldType: value as CustomFieldFormState["fieldType"],
+                }))
+              }
+              disabled={isSubmitting}
+            >
+              <SelectTrigger>
+                <SelectValue placeholder="Select field type" />
+              </SelectTrigger>
+              <SelectContent>
+                {CUSTOM_FIELD_TYPE_OPTIONS.map((option) => (
+                  <SelectItem key={option.value} value={option.value}>
+                    {option.label}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </label>
+
+          <label className="space-y-1">
+            <span className="text-sm font-semibold text-slate-900">
+              UI visible
+            </span>
+            <Select
+              value={formState.uiVisibility}
+              onValueChange={(value) =>
+                setFormState((prev) => ({
+                  ...prev,
+                  uiVisibility: value as CustomFieldFormState["uiVisibility"],
+                }))
+              }
+              disabled={isSubmitting}
+            >
+              <SelectTrigger>
+                <SelectValue placeholder="Select visibility" />
+              </SelectTrigger>
+              <SelectContent>
+                {CUSTOM_FIELD_VISIBILITY_OPTIONS.map((option) => (
+                  <SelectItem key={option.value} value={option.value}>
+                    {option.label}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </label>
+        </div>
+
+        <label className="mt-4 flex items-center gap-2 text-sm text-slate-700">
+          <input
+            type="checkbox"
+            checked={formState.required}
+            onChange={(event) =>
+              setFormState((prev) => ({
+                ...prev,
+                required: event.target.checked,
+              }))
+            }
+            disabled={isSubmitting}
+          />
+          Required
+        </label>
+      </div>
+
+      <div>
+        <p className="text-xs font-semibold uppercase tracking-wider text-slate-500">
+          Validation and defaults
+        </p>
+        <div className="mt-4 space-y-4">
+          <label className="space-y-1">
+            <span className="text-sm font-semibold text-slate-900">
+              Validation regex
+            </span>
+            <Input
+              value={formState.validationRegex}
+              onChange={(event) =>
+                setFormState((prev) => ({
+                  ...prev,
+                  validationRegex: event.target.value,
+                }))
+              }
+              placeholder="Optional. Example: ^[A-Z]{3}$"
+              disabled={
+                isSubmitting ||
+                !STRING_VALIDATION_FIELD_TYPES.has(formState.fieldType)
+              }
+            />
+            <p className="text-xs text-slate-500">
+              Supported for text/date/date-time/url fields.
+            </p>
+          </label>
+
+          <label className="space-y-1">
+            <span className="text-sm font-semibold text-slate-900">
+              Default value
+            </span>
+            <Textarea
+              value={formState.defaultValue}
+              onChange={(event) =>
+                setFormState((prev) => ({
+                  ...prev,
+                  defaultValue: event.target.value,
+                }))
+              }
+              rows={3}
+              placeholder='Optional default value. For booleans use "true"/"false"; for JSON use an object or array.'
+              disabled={isSubmitting}
+            />
+          </label>
+
+          <label className="space-y-1">
+            <span className="text-sm font-semibold text-slate-900">
+              Description
+            </span>
+            <Textarea
+              value={formState.description}
+              onChange={(event) =>
+                setFormState((prev) => ({
+                  ...prev,
+                  description: event.target.value,
+                }))
+              }
+              rows={3}
+              placeholder="Optional description used by agents and UI"
+              disabled={isSubmitting}
+            />
+          </label>
+        </div>
+      </div>
+
+      <div>
+        <div className="flex flex-wrap items-center justify-between gap-2">
+          <p className="text-xs font-semibold uppercase tracking-wider text-slate-500">
+            Board bindings
+          </p>
+          <span className="text-xs text-slate-500">
+            {selectedBoardIds.size} selected
+          </span>
+        </div>
+        <div className="mt-4 space-y-2">
+          <Input
+            value={boardSearch}
+            onChange={(event) => setBoardSearch(event.target.value)}
+            placeholder="Search boards..."
+            disabled={isSubmitting}
+          />
+          <div className="max-h-64 overflow-auto rounded-xl border border-slate-200 bg-slate-50/40">
+            {boardsLoading ? (
+              <div className="px-4 py-6 text-sm text-slate-500">
+                Loading boards…
+              </div>
+            ) : boardsError ? (
+              <div className="px-4 py-6 text-sm text-rose-700">
+                {boardsError}
+              </div>
+            ) : filteredBoards.length === 0 ? (
+              <div className="px-4 py-6 text-sm text-slate-500">
+                No boards found.
+              </div>
+            ) : (
+              <ul className="divide-y divide-slate-200">
+                {filteredBoards.map((board) => {
+                  const checked = selectedBoardIds.has(board.id);
+                  return (
+                    <li key={board.id} className="px-4 py-3">
+                      <label className="flex cursor-pointer items-start gap-3">
+                        <input
+                          type="checkbox"
+                          className="mt-1 h-4 w-4 rounded border-slate-300 text-blue-600"
+                          checked={checked}
+                          onChange={() => {
+                            setSelectedBoardIds((prev) => {
+                              const next = new Set(prev);
+                              if (next.has(board.id)) {
+                                next.delete(board.id);
+                              } else {
+                                next.add(board.id);
+                              }
+                              return next;
+                            });
+                          }}
+                          disabled={isSubmitting}
+                        />
+                        <div className="min-w-0">
+                          <p className="truncate text-sm font-medium text-slate-900">
+                            {board.name}
+                          </p>
+                          <p className="mt-1 text-xs text-slate-500">
+                            {board.slug}
+                          </p>
+                        </div>
+                      </label>
+                    </li>
+                  );
+                })}
+              </ul>
+            )}
+          </div>
+          <p className="text-xs text-slate-500">
+            Required. The custom field appears on tasks in selected boards.
+          </p>
+        </div>
+      </div>
+
+      {submitError ? (
+        <p className="text-sm text-rose-600">{submitError}</p>
+      ) : null}
+      <div className="flex items-center gap-2">
+        <Link
+          href={cancelHref}
+          className={buttonVariants({ variant: "outline" })}
+          aria-disabled={isSubmitting}
+        >
+          Cancel
+        </Link>
+        <Button type="submit" disabled={isSubmitting}>
+          {isSubmitting ? submittingLabel : submitLabel}
+        </Button>
+      </div>
+    </form>
+  );
+}
diff --git a/frontend/src/components/custom-fields/CustomFieldsTable.tsx b/frontend/src/components/custom-fields/CustomFieldsTable.tsx
index 6315ff33..1fd3baf3 100644
--- a/frontend/src/components/custom-fields/CustomFieldsTable.tsx
+++ b/frontend/src/components/custom-fields/CustomFieldsTable.tsx
@@ -16,6 +16,7 @@ import {
 } from "@/components/tables/DataTable";
 import { dateCell } from "@/components/tables/cell-formatters";
 import type { TaskCustomFieldDefinitionRead } from "@/api/generated/model";
+import { formatCustomFieldDefaultValue } from "./custom-field-form-utils";
 
 type CustomFieldsTableProps = {
   fields: TaskCustomFieldDefinitionRead[];
@@ -49,16 +50,6 @@ const DEFAULT_EMPTY_ICON = (
   </svg>
 );
 
-const formatDefaultValue = (value: unknown): string => {
-  if (value === null || value === undefined) return "";
-  if (typeof value === "string") return value;
-  try {
-    return JSON.stringify(value);
-  } catch {
-    return String(value);
-  }
-};
-
 export function CustomFieldsTable({
   fields,
   isLoading = false,
@@ -131,7 +122,7 @@ export function CustomFieldsTable({
         enableSorting: false,
         cell: ({ row }) => (
           <p className="font-mono text-xs break-all text-slate-700">
-            {formatDefaultValue(row.original.default_value) || "—"}
+            {formatCustomFieldDefaultValue(row.original.default_value) || "—"}
           </p>
         ),
       },
diff --git a/frontend/src/components/custom-fields/custom-field-form-types.ts b/frontend/src/components/custom-fields/custom-field-form-types.ts
new file mode 100644
index 00000000..9f2d1863
--- /dev/null
+++ b/frontend/src/components/custom-fields/custom-field-form-types.ts
@@ -0,0 +1,63 @@
+import type {
+  TaskCustomFieldDefinitionReadFieldType,
+  TaskCustomFieldDefinitionReadUiVisibility,
+} from "@/api/generated/model";
+
+export type CustomFieldType = TaskCustomFieldDefinitionReadFieldType;
+export type CustomFieldVisibility = TaskCustomFieldDefinitionReadUiVisibility;
+
+export type CustomFieldFormMode = "create" | "edit";
+
+export type CustomFieldFormState = {
+  fieldKey: string;
+  label: string;
+  fieldType: CustomFieldType;
+  uiVisibility: CustomFieldVisibility;
+  validationRegex: string;
+  description: string;
+  required: boolean;
+  defaultValue: string;
+};
+
+export const DEFAULT_CUSTOM_FIELD_FORM_STATE: CustomFieldFormState = {
+  fieldKey: "",
+  label: "",
+  fieldType: "text",
+  uiVisibility: "always",
+  validationRegex: "",
+  description: "",
+  required: false,
+  defaultValue: "",
+};
+
+export const CUSTOM_FIELD_TYPE_OPTIONS: ReadonlyArray<{
+  value: CustomFieldType;
+  label: string;
+}> = [
+  { value: "text", label: "Text" },
+  { value: "text_long", label: "Text (long)" },
+  { value: "integer", label: "Integer" },
+  { value: "decimal", label: "Decimal" },
+  { value: "boolean", label: "Boolean (true/false)" },
+  { value: "date", label: "Date" },
+  { value: "date_time", label: "Date & time" },
+  { value: "url", label: "URL" },
+  { value: "json", label: "JSON" },
+];
+
+export const CUSTOM_FIELD_VISIBILITY_OPTIONS: ReadonlyArray<{
+  value: CustomFieldVisibility;
+  label: string;
+}> = [
+  { value: "always", label: "Always" },
+  { value: "if_set", label: "If set" },
+  { value: "hidden", label: "Hidden" },
+];
+
+export const STRING_VALIDATION_FIELD_TYPES = new Set<CustomFieldType>([
+  "text",
+  "text_long",
+  "date",
+  "date_time",
+  "url",
+]);
diff --git a/frontend/src/components/custom-fields/custom-field-form-utils.test.ts b/frontend/src/components/custom-fields/custom-field-form-utils.test.ts
new file mode 100644
index 00000000..19739597
--- /dev/null
+++ b/frontend/src/components/custom-fields/custom-field-form-utils.test.ts
@@ -0,0 +1,167 @@
+import { describe, expect, it } from "vitest";
+
+import type { TaskCustomFieldDefinitionRead } from "@/api/generated/model";
+import { DEFAULT_CUSTOM_FIELD_FORM_STATE } from "./custom-field-form-types";
+import {
+  buildCustomFieldUpdatePayload,
+  createCustomFieldPayload,
+  formatCustomFieldDefaultValue,
+  normalizeCustomFieldFormInput,
+  parseCustomFieldDefaultValue,
+} from "./custom-field-form-utils";
+
+const buildField = (
+  overrides: Partial<TaskCustomFieldDefinitionRead> = {},
+): TaskCustomFieldDefinitionRead => ({
+  id: "field-1",
+  organization_id: "org-1",
+  field_key: "client_name",
+  label: "Client Name",
+  field_type: "text",
+  ui_visibility: "always",
+  board_ids: ["board-1"],
+  required: false,
+  description: "Client display name",
+  default_value: "Acme",
+  validation_regex: null,
+  created_at: "2026-01-01T00:00:00Z",
+  updated_at: "2026-01-01T00:00:00Z",
+  ...overrides,
+});
+
+describe("parseCustomFieldDefaultValue", () => {
+  it("parses primitive and json field types", () => {
+    expect(parseCustomFieldDefaultValue("integer", "42")).toEqual({
+      value: 42,
+      error: null,
+    });
+    expect(parseCustomFieldDefaultValue("decimal", "-12.5")).toEqual({
+      value: -12.5,
+      error: null,
+    });
+    expect(parseCustomFieldDefaultValue("boolean", "TRUE")).toEqual({
+      value: true,
+      error: null,
+    });
+    expect(parseCustomFieldDefaultValue("json", '{"a":1}')).toEqual({
+      value: { a: 1 },
+      error: null,
+    });
+  });
+
+  it("returns validation errors for invalid defaults", () => {
+    expect(parseCustomFieldDefaultValue("integer", "42.5").error).toMatch(
+      /valid integer/i,
+    );
+    expect(parseCustomFieldDefaultValue("boolean", "yes").error).toMatch(
+      /true or false/i,
+    );
+    expect(parseCustomFieldDefaultValue("json", '"string"').error).toMatch(
+      /object or array/i,
+    );
+  });
+});
+
+describe("normalizeCustomFieldFormInput", () => {
+  it("validates create requirements", () => {
+    const result = normalizeCustomFieldFormInput({
+      mode: "create",
+      formState: {
+        ...DEFAULT_CUSTOM_FIELD_FORM_STATE,
+        label: "Client Name",
+      },
+      selectedBoardIds: [],
+    });
+
+    expect(result.value).toBeNull();
+    expect(result.error).toBe("Field key is required.");
+  });
+
+  it("normalizes and trims valid create input", () => {
+    const result = normalizeCustomFieldFormInput({
+      mode: "create",
+      formState: {
+        ...DEFAULT_CUSTOM_FIELD_FORM_STATE,
+        fieldKey: "  client_name ",
+        label: " Client Name ",
+        fieldType: "integer",
+        uiVisibility: "if_set",
+        validationRegex: "",
+        description: " Primary client ",
+        required: true,
+        defaultValue: " 7 ",
+      },
+      selectedBoardIds: ["board-1", "board-2"],
+    });
+
+    expect(result.error).toBeNull();
+    expect(result.value).toEqual({
+      fieldKey: "client_name",
+      label: "Client Name",
+      fieldType: "integer",
+      uiVisibility: "if_set",
+      validationRegex: null,
+      description: "Primary client",
+      required: true,
+      defaultValue: 7,
+      boardIds: ["board-1", "board-2"],
+    });
+  });
+});
+
+describe("payload helpers", () => {
+  it("builds create payload from normalized values", () => {
+    const payload = createCustomFieldPayload({
+      fieldKey: "client_name",
+      label: "Client Name",
+      fieldType: "text",
+      uiVisibility: "always",
+      validationRegex: "^[A-Z]+$",
+      description: "Display name",
+      required: false,
+      defaultValue: "ACME",
+      boardIds: ["board-1"],
+    });
+
+    expect(payload).toEqual({
+      field_key: "client_name",
+      label: "Client Name",
+      field_type: "text",
+      ui_visibility: "always",
+      validation_regex: "^[A-Z]+$",
+      description: "Display name",
+      required: false,
+      default_value: "ACME",
+      board_ids: ["board-1"],
+    });
+  });
+
+  it("only includes changed fields in update payload", () => {
+    const field = buildField();
+    const updates = buildCustomFieldUpdatePayload(field, {
+      fieldKey: "client_name",
+      label: "Client Name",
+      fieldType: "text",
+      uiVisibility: "always",
+      validationRegex: null,
+      description: "Client display name",
+      required: true,
+      defaultValue: "ACME",
+      boardIds: ["board-1"],
+    });
+
+    expect(updates).toEqual({
+      required: true,
+      default_value: "ACME",
+    });
+  });
+});
+
+describe("formatCustomFieldDefaultValue", () => {
+  it("formats objects as minified or pretty json", () => {
+    expect(formatCustomFieldDefaultValue({ a: 1 })).toBe('{"a":1}');
+    expect(formatCustomFieldDefaultValue({ a: 1 }, { pretty: true })).toBe(
+      '{\n  "a": 1\n}',
+    );
+  });
+});
diff --git a/frontend/src/components/custom-fields/custom-field-form-utils.ts b/frontend/src/components/custom-fields/custom-field-form-utils.ts
new file mode 100644
index 00000000..1bcb2495
--- /dev/null
+++ b/frontend/src/components/custom-fields/custom-field-form-utils.ts
@@ -0,0 +1,273 @@
+import type {
+  BoardRead,
+  TaskCustomFieldDefinitionCreate,
+  TaskCustomFieldDefinitionRead,
+  TaskCustomFieldDefinitionUpdate,
+} from "@/api/generated/model";
+import { ApiError } from "@/api/mutator";
+
+import {
+  type CustomFieldFormMode,
+  type CustomFieldFormState,
+  type CustomFieldType,
+  STRING_VALIDATION_FIELD_TYPES,
+} from "./custom-field-form-types";
+
+export type ParsedDefaultValue = {
+  value: unknown | null;
+  error: string | null;
+};
+
+export type NormalizedCustomFieldFormValues = {
+  fieldKey: string;
+  label: string;
+  fieldType: CustomFieldType;
+  uiVisibility: CustomFieldFormState["uiVisibility"];
+  validationRegex: string | null;
+  description: string | null;
+  required: boolean;
+  defaultValue: unknown | null;
+  boardIds: string[];
+};
+
+type NormalizeCustomFieldFormInputArgs = {
+  mode: CustomFieldFormMode;
+  formState: CustomFieldFormState;
+  selectedBoardIds: Iterable<string>;
+};
+
+type NormalizeCustomFieldFormInputResult =
+  | { value: NormalizedCustomFieldFormValues; error: null }
+  | { value: null; error: string };
+
+const canonicalJson = (value: unknown): string =>
+  JSON.stringify(value) ?? "undefined";
+
+const areSortedStringArraysEqual = (
+  left: readonly string[],
+  right: readonly string[],
+): boolean =>
+  left.length === right.length &&
+  left.every((value, index) => value === right[index]);
+
+export const parseCustomFieldDefaultValue = (
+  fieldType: CustomFieldType,
+  value: string,
+): ParsedDefaultValue => {
+  const trimmed = value.trim();
+  if (!trimmed) return { value: null, error: null };
+
+  if (fieldType === "text" || fieldType === "text_long") {
+    return { value: trimmed, error: null };
+  }
+
+  if (fieldType === "integer") {
+    if (!/^-?\d+$/.test(trimmed)) {
+      return { value: null, error: "Default value must be a valid integer." };
+    }
+    return { value: Number.parseInt(trimmed, 10), error: null };
+  }
+
+  if (fieldType === "decimal") {
+    if (!/^-?\d+(\.\d+)?$/.test(trimmed)) {
+      return { value: null, error: "Default value must be a valid decimal." };
+    }
+    return { value: Number.parseFloat(trimmed), error: null };
+  }
+
+  if (fieldType === "boolean") {
+    if (trimmed.toLowerCase() === "true") return { value: true, error: null };
+    if (trimmed.toLowerCase() === "false") return { value: false, error: null };
+    return { value: null, error: "Default value must be true or false." };
+  }
+
+  if (
+    fieldType === "date" ||
+    fieldType === "date_time" ||
+    fieldType === "url"
+  ) {
+    return { value: trimmed, error: null };
+  }
+
+  if (fieldType === "json") {
+    try {
+      const parsed = JSON.parse(trimmed);
+      if (parsed === null || typeof parsed !== "object") {
+        return {
+          value: null,
+          error: "Default value must be valid JSON (object or array).",
+        };
+      }
+      return { value: parsed, error: null };
+    } catch {
+      return {
+        value: null,
+        error: "Default value must be valid JSON (object or array).",
+      };
+    }
+  }
+
+  try {
+    return { value: JSON.parse(trimmed), error: null };
+  } catch {
+    return { value: trimmed, error: null };
+  }
+};
+
+export const formatCustomFieldDefaultValue = (
+  value: unknown,
+  options: { pretty?: boolean } = {},
+): string => {
+  if (value === null || value === undefined) return "";
+  if (typeof value === "string") return value;
+  try {
+    return options.pretty
+      ? JSON.stringify(value, null, 2)
+      : JSON.stringify(value);
+  } catch {
+    return String(value);
+  }
+};
+
+export const filterBoardsBySearch = (
+  boards: BoardRead[],
+  query: string,
+): BoardRead[] => {
+  const normalizedQuery = query.trim().toLowerCase();
+  if (!normalizedQuery) return boards;
+  return boards.filter(
+    (board) =>
+      board.name.toLowerCase().includes(normalizedQuery) ||
+      board.slug.toLowerCase().includes(normalizedQuery),
+  );
+};
+
+export const normalizeCustomFieldFormInput = ({
+  mode,
+  formState,
+  selectedBoardIds,
+}: NormalizeCustomFieldFormInputArgs): NormalizeCustomFieldFormInputResult => {
+  const trimmedFieldKey = formState.fieldKey.trim();
+  const trimmedLabel = formState.label.trim();
+  const trimmedValidationRegex = formState.validationRegex.trim();
+  const boardIds = Array.from(selectedBoardIds);
+
+  if (mode === "create" && !trimmedFieldKey) {
+    return { value: null, error: "Field key is required." };
+  }
+  if (!trimmedLabel) return { value: null, error: "Label is required." };
+  if (boardIds.length === 0) {
+    return { value: null, error: "Select at least one board." };
+  }
+  if (
+    trimmedValidationRegex &&
+    !STRING_VALIDATION_FIELD_TYPES.has(formState.fieldType)
+  ) {
+    return {
+      value: null,
+      error: "Validation regex is only supported for string field types.",
+    };
+  }
+
+  const parsedDefaultValue = parseCustomFieldDefaultValue(
+    formState.fieldType,
+    formState.defaultValue,
+  );
+  if (parsedDefaultValue.error) {
+    return { value: null, error: parsedDefaultValue.error };
+  }
+
+  return {
+    value: {
+      fieldKey: trimmedFieldKey,
+      label: trimmedLabel,
+      fieldType: formState.fieldType,
+      uiVisibility: formState.uiVisibility,
+      validationRegex: trimmedValidationRegex || null,
+      description: formState.description.trim() || null,
+      required: formState.required,
+      defaultValue: parsedDefaultValue.value,
+      boardIds,
+    },
+    error: null,
+  };
+};
+
+export const createCustomFieldPayload = (
+  values: NormalizedCustomFieldFormValues,
+): TaskCustomFieldDefinitionCreate => ({
+  field_key: values.fieldKey,
+  label: values.label,
+  field_type: values.fieldType,
+  ui_visibility: values.uiVisibility,
+  validation_regex: values.validationRegex,
+  description: values.description,
+  required: values.required,
+  default_value: values.defaultValue,
+  board_ids: values.boardIds,
+});
+
+export const buildCustomFieldUpdatePayload = (
+  field: TaskCustomFieldDefinitionRead,
+  values: NormalizedCustomFieldFormValues,
+): TaskCustomFieldDefinitionUpdate => {
+  const updates: TaskCustomFieldDefinitionUpdate = {};
+
+  if (values.label !== (field.label ?? field.field_key)) {
+    updates.label = values.label;
+  }
+  if (values.fieldType !== (field.field_type ?? "text")) {
+    updates.field_type = values.fieldType;
+  }
+  if (values.uiVisibility !== (field.ui_visibility ?? "always")) {
+    updates.ui_visibility = values.uiVisibility;
+  }
+  if (values.validationRegex !== (field.validation_regex ?? null)) {
+    updates.validation_regex = values.validationRegex;
+  }
+  if (values.description !== (field.description ?? null)) {
+    updates.description = values.description;
+  }
+  if (values.required !== (field.required === true)) {
+    updates.required = values.required;
+  }
+  if (
+    canonicalJson(values.defaultValue) !== canonicalJson(field.default_value)
+  ) {
+    updates.default_value = values.defaultValue;
+  }
+
+  const currentBoardIds = [...(field.board_ids ?? [])].sort();
+  const nextBoardIds = [...values.boardIds].sort();
+  if (!areSortedStringArraysEqual(currentBoardIds, nextBoardIds)) {
+    updates.board_ids = values.boardIds;
+  }
+
+  return updates;
+};
+
+export const deriveFormStateFromCustomField = (
+  field: TaskCustomFieldDefinitionRead,
+): CustomFieldFormState => ({
+  fieldKey: field.field_key,
+  label: field.label ?? field.field_key,
+  fieldType: field.field_type ?? "text",
+  uiVisibility: field.ui_visibility ?? "always",
+  validationRegex: field.validation_regex ?? "",
+  description: field.description ?? "",
+  required: field.required === true,
+  defaultValue: formatCustomFieldDefaultValue(field.default_value, {
+    pretty: true,
+  }),
+});
+
+export const extractApiErrorMessage = (
+  error: unknown,
+  fallback: string,
+): string => {
+  if (error instanceof ApiError) return error.message || fallback;
+  if (error instanceof Error) return error.message || fallback;
+  const detail = (error as { detail?: unknown } | null | undefined)?.detail;
+  if (detail) return String(detail);
+  return fallback;
+};