diff --git a/backend/.env.example b/backend/.env.example
index 12de11d2..aad21354 100644
--- a/backend/.env.example
+++ b/backend/.env.example
@@ -7,6 +7,7 @@ REQUEST_LOG_INCLUDE_HEALTH=false
 DATABASE_URL=postgresql+psycopg://postgres:postgres@localhost:5432/mission_control
 # For remote access, set this to your UI origin (e.g. http://<server-ip>:3000 or https://mc.example.com).
 CORS_ORIGINS=http://localhost:3000
+# REQUIRED for gateway provisioning/agent heartbeats. Must be reachable by gateway runtime.
 BASE_URL=
 # Security response headers (blank values disable each header).
 SECURITY_HEADER_X_CONTENT_TYPE_OPTIONS=
diff --git a/backend/.env.test b/backend/.env.test
index 70f9a7ee..2d22385a 100644
--- a/backend/.env.test
+++ b/backend/.env.test
@@ -13,7 +13,7 @@ REQUEST_LOG_INCLUDE_HEALTH=false
 # Local backend -> local Postgres (adjust host/port if needed)
 DATABASE_URL=postgresql+psycopg://postgres:postgres@localhost:5432/mission_control_test
 CORS_ORIGINS=http://localhost:3000
-BASE_URL=
+BASE_URL=http://localhost:8000
 
 # Auth mode: local for test/dev
 AUTH_MODE=local
diff --git a/backend/README.md b/backend/README.md
index 03684367..6343cebd 100644
--- a/backend/README.md
+++ b/backend/README.md
@@ -57,7 +57,7 @@ A starter file exists at `backend/.env.example`.
     `postgresql+psycopg://postgres:postgres@localhost:5432/mission_control`
 - `CORS_ORIGINS` (comma-separated)
   - Example: `http://localhost:3000`
-- `BASE_URL` (optional)
+- `BASE_URL` (required for gateway provisioning/agent heartbeat templates; no fallback)
 
 ### Database lifecycle
 
diff --git a/backend/app/api/board_group_memory.py b/backend/app/api/board_group_memory.py
index d965c718..b9b1fd63 100644
--- a/backend/app/api/board_group_memory.py
+++ b/backend/app/api/board_group_memory.py
@@ -331,7 +331,7 @@ async def _notify_group_memory_targets(
     if len(snippet) > MAX_SNIPPET_LENGTH:
         snippet = f"{snippet[: MAX_SNIPPET_LENGTH - 3]}..."
 
-    base_url = settings.base_url or "http://localhost:8000"
+    base_url = settings.base_url
 
     context = _NotifyGroupContext(
         session=session,
diff --git a/backend/app/api/board_memory.py b/backend/app/api/board_memory.py
index bf234be3..d04ea3f5 100644
--- a/backend/app/api/board_memory.py
+++ b/backend/app/api/board_memory.py
@@ -191,7 +191,7 @@ async def _notify_chat_targets(
     snippet = memory.content.strip()
     if len(snippet) > MAX_SNIPPET_LENGTH:
         snippet = f"{snippet[: MAX_SNIPPET_LENGTH - 3]}..."
-    base_url = settings.base_url or "http://localhost:8000"
+    base_url = settings.base_url
     for agent in targets.values():
         if not agent.openclaw_session_id:
             continue
diff --git a/backend/app/api/board_onboarding.py b/backend/app/api/board_onboarding.py
index e0ac1a7b..51be333e 100644
--- a/backend/app/api/board_onboarding.py
+++ b/backend/app/api/board_onboarding.py
@@ -229,7 +229,7 @@ async def start_onboarding(
         return onboarding
 
     dispatcher = BoardOnboardingMessagingService(session)
-    base_url = settings.base_url or "http://localhost:8000"
+    base_url = settings.base_url
     prompt = (
         "BOARD ONBOARDING REQUEST\n\n"
         f"Board Name: {board.name}\n"
diff --git a/backend/app/core/config.py b/backend/app/core/config.py
index 67822b57..46d20683 100644
--- a/backend/app/core/config.py
+++ b/backend/app/core/config.py
@@ -4,6 +4,7 @@ from __future__ import annotations
 
 from pathlib import Path
 from typing import Self
+from urllib.parse import urlparse
 
 from pydantic import Field, model_validator
 from pydantic_settings import BaseSettings, SettingsConfigDict
@@ -48,7 +49,7 @@ class Settings(BaseSettings):
     clerk_leeway: float = 10.0
 
     cors_origins: str = ""
-    base_url: str = ""
+    base_url: str
     # Security response headers (blank disables header injection)
     security_header_x_content_type_options: str = ""
     security_header_x_frame_options: str = ""
@@ -93,6 +94,15 @@ class Settings(BaseSettings):
                 raise ValueError(
                     "LOCAL_AUTH_TOKEN must be at least 50 characters and non-placeholder when AUTH_MODE=local.",
                 )
+        base_url = self.base_url.strip()
+        if not base_url:
+            raise ValueError("BASE_URL must be set and non-empty.")
+        parsed_base_url = urlparse(base_url)
+        if parsed_base_url.scheme not in {"http", "https"} or not parsed_base_url.netloc:
+            raise ValueError(
+                "BASE_URL must be an absolute http(s) URL (e.g. http://localhost:8000).",
+            )
+        self.base_url = base_url.rstrip("/")
         # In dev, default to applying Alembic migrations at startup to avoid
         # schema drift (e.g. missing newly-added columns).
         if "db_auto_migrate" not in self.model_fields_set and self.environment == "dev":
diff --git a/backend/app/services/openclaw/coordination_service.py b/backend/app/services/openclaw/coordination_service.py
index 8b6d8365..6384ecd8 100644
--- a/backend/app/services/openclaw/coordination_service.py
+++ b/backend/app/services/openclaw/coordination_service.py
@@ -93,7 +93,7 @@ class GatewayCoordinationService(AbstractGatewayMessagingService):
         reply_tags: list[str] | None,
         reply_source: str | None,
     ) -> str:
-        base_url = settings.base_url or "http://localhost:8000"
+        base_url = settings.base_url
         header = "GATEWAY MAIN QUESTION" if kind == "question" else "GATEWAY MAIN HANDOFF"
         correlation = correlation_id.strip() if correlation_id else ""
         correlation_line = f"Correlation ID: {correlation}\n" if correlation else ""
@@ -440,7 +440,7 @@ class GatewayCoordinationService(AbstractGatewayMessagingService):
         tags = payload.reply_tags or ["gateway_main", "user_reply"]
         tags_json = json.dumps(tags)
         reply_source = payload.reply_source or "user_via_gateway_main"
-        base_url = settings.base_url or "http://localhost:8000"
+        base_url = settings.base_url
         message = (
             "LEAD REQUEST: ASK USER\n"
             f"Board: {board.name}\n"
diff --git a/backend/app/services/openclaw/provisioning.py b/backend/app/services/openclaw/provisioning.py
index 3a1d76f2..f49fecf6 100644
--- a/backend/app/services/openclaw/provisioning.py
+++ b/backend/app/services/openclaw/provisioning.py
@@ -370,7 +370,7 @@ def _build_context(
     workspace_root = gateway.workspace_root
     workspace_path = _workspace_path(agent, workspace_root)
     session_key = agent.openclaw_session_id or ""
-    base_url = settings.base_url or "REPLACE_WITH_BASE_URL"
+    base_url = settings.base_url
     main_session_key = GatewayAgentIdentity.session_key(gateway)
     identity_context = _identity_context(agent)
     user_context = _user_context(user)
@@ -411,7 +411,7 @@ def _build_main_context(
     auth_token: str,
     user: User | None,
 ) -> dict[str, str]:
-    base_url = settings.base_url or "REPLACE_WITH_BASE_URL"
+    base_url = settings.base_url
     identity_context = _identity_context(agent)
     user_context = _user_context(user)
     return {
diff --git a/backend/tests/conftest.py b/backend/tests/conftest.py
index e522fc29..a9022efe 100644
--- a/backend/tests/conftest.py
+++ b/backend/tests/conftest.py
@@ -13,3 +13,4 @@ if str(ROOT) not in sys.path:
 # defaults during import-time settings initialization, regardless of shell env.
 os.environ["AUTH_MODE"] = "local"
 os.environ["LOCAL_AUTH_TOKEN"] = "test-local-token-0123456789-0123456789-0123456789x"
+os.environ["BASE_URL"] = "http://localhost:8000"
diff --git a/backend/tests/test_config_auth_mode.py b/backend/tests/test_config_auth_mode.py
index 1f913302..6c6ac1fc 100644
--- a/backend/tests/test_config_auth_mode.py
+++ b/backend/tests/test_config_auth_mode.py
@@ -9,6 +9,8 @@ from pydantic import ValidationError
 from app.core.auth_mode import AuthMode
 from app.core.config import Settings
 
+BASE_URL = "http://localhost:8000"
+
 
 def test_local_mode_requires_non_empty_token() -> None:
     with pytest.raises(
@@ -19,6 +21,7 @@ def test_local_mode_requires_non_empty_token() -> None:
             _env_file=None,
             auth_mode=AuthMode.LOCAL,
             local_auth_token="",
+            base_url=BASE_URL,
         )
 
 
@@ -31,6 +34,7 @@ def test_local_mode_requires_minimum_length() -> None:
             _env_file=None,
             auth_mode=AuthMode.LOCAL,
             local_auth_token="x" * 49,
+            base_url=BASE_URL,
         )
 
 
@@ -43,6 +47,7 @@ def test_local_mode_rejects_placeholder_token() -> None:
             _env_file=None,
             auth_mode=AuthMode.LOCAL,
             local_auth_token="change-me",
+            base_url=BASE_URL,
         )
 
 
@@ -52,6 +57,7 @@ def test_local_mode_accepts_real_token() -> None:
         _env_file=None,
         auth_mode=AuthMode.LOCAL,
         local_auth_token=token,
+        base_url=BASE_URL,
     )
 
     assert settings.auth_mode == AuthMode.LOCAL
@@ -67,4 +73,65 @@ def test_clerk_mode_requires_secret_key() -> None:
             _env_file=None,
             auth_mode=AuthMode.CLERK,
             clerk_secret_key="",
+            base_url=BASE_URL,
         )
+
+
+def test_base_url_required() -> None:
+    with pytest.raises(
+        ValidationError,
+        match="BASE_URL must be set and non-empty",
+    ):
+        Settings(
+            _env_file=None,
+            auth_mode=AuthMode.CLERK,
+            clerk_secret_key="sk_test",
+            base_url="  ",
+        )
+
+
+def test_base_url_field_is_required(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.delenv("BASE_URL", raising=False)
+
+    with pytest.raises(ValidationError) as exc_info:
+        Settings(
+            _env_file=None,
+            auth_mode=AuthMode.CLERK,
+            clerk_secret_key="sk_test",
+        )
+
+    text = str(exc_info.value)
+    assert "base_url" in text
+    assert "Field required" in text
+
+
+@pytest.mark.parametrize(
+    "base_url",
+    [
+        "localhost:8000",
+        "ws://localhost:8000",
+    ],
+)
+def test_base_url_requires_absolute_http_url(base_url: str) -> None:
+    with pytest.raises(
+        ValidationError,
+        match="BASE_URL must be an absolute http\\(s\\) URL",
+    ):
+        Settings(
+            _env_file=None,
+            auth_mode=AuthMode.CLERK,
+            clerk_secret_key="sk_test",
+            base_url=base_url,
+        )
+
+
+def test_base_url_is_normalized_without_trailing_slash() -> None:
+    token = "a" * 50
+    settings = Settings(
+        _env_file=None,
+        auth_mode=AuthMode.LOCAL,
+        local_auth_token=token,
+        base_url="http://localhost:8000/ ",
+    )
+
+    assert settings.base_url == BASE_URL