diff --git a/src/framex/driver/ingress.py b/src/framex/driver/ingress.py
index 1739184..19a859d 100644
--- a/src/framex/driver/ingress.py
+++ b/src/framex/driver/ingress.py
@@ -1,3 +1,4 @@
+import re
 from collections.abc import Callable
 from enum import Enum
 from typing import Any
@@ -123,7 +124,7 @@ def _verify_api_key(request: Request, api_key: str | None = Depends(api_key_head
 
                 dependencies.append(Depends(_verify_api_key))
 
-            app.add_api_route(
+            self.add_api_route(
                 path,
                 route_handler,
                 methods=methods,
@@ -146,3 +147,24 @@ async def inner(self) -> str:  # pragma: no cover
 
     def __repr__(self):
         return BACKEND_NAME
+
+    def add_api_route(
+        self,
+        path: str,
+        endpoint: Callable[..., Any],
+        *,
+        methods: list[str] | None = None,
+        **kwargs: Any,
+    ) -> None:
+        method_set: set[str] = {m.upper() for m in methods} if methods else {"GET"}
+        norm_path = re.sub(r"\{[^}]+\}", "{}", path)
+
+        for route in app.routes:
+            if (
+                isinstance(route, APIRoute)
+                and re.sub(r"\{[^}]+\}", "{}", route.path) == norm_path
+                and route.methods & method_set
+            ):
+                raise RuntimeError(f"Duplicate API route: {sorted(method_set)} {norm_path}")
+
+        app.add_api_route(path, endpoint, methods=list(method_set), **kwargs)
diff --git a/tests/driver/test_ingress.py b/tests/driver/test_ingress.py
new file mode 100644
index 0000000..fd1a5aa
--- /dev/null
+++ b/tests/driver/test_ingress.py
@@ -0,0 +1,104 @@
+from unittest.mock import Mock, patch
+
+import pytest
+from fastapi.routing import APIRoute
+from starlette.routing import Route
+
+from framex.driver.ingress import APIIngress
+
+# ---------- helpers ----------
+
+
+def make_route(path: str, methods: set[str]) -> APIRoute:
+    route = Mock(spec=APIRoute)
+    route.path = path
+    route.methods = methods
+    return route
+
+
+# ---------- fixtures ----------
+
+
+@pytest.fixture
+def mock_app():
+    with patch("framex.driver.ingress.app") as app:
+        app.routes = []
+        app.add_api_route = Mock()
+        yield app
+
+
+@pytest.fixture
+def ingress():
+    return APIIngress.__new__(APIIngress)
+
+
+# ---------- tests ----------
+
+
+def test_add_first_route_success(ingress, mock_app):
+    endpoint = Mock()
+
+    ingress.add_api_route("/users", endpoint, methods=["GET"])
+
+    mock_app.add_api_route.assert_called_once_with("/users", endpoint, methods=["GET"])
+
+
+@pytest.mark.parametrize(
+    ("existing_path", "new_path"),
+    [
+        ("/users/{id}", "/users/{id}"),
+        ("/users/{id}", "/users/{user_id}"),
+        ("/users/{uid}/posts/{pid}", "/users/{id}/posts/{post_id}"),
+    ],
+)
+def test_duplicate_path_same_method_raises(ingress, mock_app, existing_path, new_path):
+    mock_app.routes = [make_route(existing_path, {"GET"})]
+
+    with pytest.raises(RuntimeError, match=r"Duplicate API route"):
+        ingress.add_api_route(new_path, Mock(), methods=["GET"])
+
+
+def test_same_path_different_method_allowed(ingress, mock_app):
+    mock_app.routes = [make_route("/users/{id}", {"GET"})]
+
+    ingress.add_api_route("/users/{id}", Mock(), methods=["POST"])
+
+    mock_app.add_api_route.assert_called_once()
+
+
+def test_overlapping_methods_raises(ingress, mock_app):
+    mock_app.routes = [make_route("/users", {"GET", "POST"})]
+
+    with pytest.raises(RuntimeError):
+        ingress.add_api_route("/users", Mock(), methods=["POST", "PUT"])
+
+
+def test_case_insensitive_methods(ingress, mock_app):
+    mock_app.routes = [make_route("/users", {"GET"})]
+
+    with pytest.raises(RuntimeError):
+        ingress.add_api_route("/users", Mock(), methods=["get"])
+
+
+def test_non_api_route_is_ignored(ingress, mock_app):
+    non_api_route = Mock(spec=Route)
+    non_api_route.path = "/users/{id}"
+    mock_app.routes = [non_api_route]
+
+    ingress.add_api_route("/users/{id}", Mock(), methods=["GET"])
+
+    mock_app.add_api_route.assert_called_once()
+
+
+def test_kwargs_are_passed_through(ingress, mock_app):
+    ingress.add_api_route(
+        "/users",
+        Mock(),
+        methods=["GET"],
+        tags=["users"],
+        response_class=Mock(),
+    )
+
+    _, kwargs = mock_app.add_api_route.call_args
+    assert kwargs["tags"] == ["users"]
+    assert "response_class" in kwargs