diff --git a/backend/apps/agent_app.py b/backend/apps/agent_app.py
index 0a97f3845..9b6dc2b7b 100644
--- a/backend/apps/agent_app.py
+++ b/backend/apps/agent_app.py
@@ -61,8 +61,11 @@ async def agent_run_api(agent_request: AgentRequest, http_request: Request, auth
         )
     except Exception as e:
         logger.error(f"Agent run error: {str(e)}")
+        # Only expose actual error in debug mode for better diagnosis
+        # Keep generic message in normal mode for user experience
+        error_detail = str(e) if agent_request.is_debug else "Agent run error."
         raise HTTPException(
-            status_code=HTTPStatus.INTERNAL_SERVER_ERROR, detail="Agent run error.")
+            status_code=HTTPStatus.INTERNAL_SERVER_ERROR, detail=error_detail)
 
 
 @agent_runtime_router.get("/stop/{conversation_id}")
diff --git a/test/backend/app/test_agent_app.py b/test/backend/app/test_agent_app.py
index 427d7cc58..55a21dfa3 100644
--- a/test/backend/app/test_agent_app.py
+++ b/test/backend/app/test_agent_app.py
@@ -187,6 +187,56 @@ async def mock_stream():
     assert "data: chunk2" in content
 
 
+async def test_agent_run_api_error_debug_mode(mocker, mock_auth_header):
+    """Test agent_run_api error case in debug mode - should expose actual error."""
+    mock_run_agent_stream = mocker.patch(
+        "apps.agent_app.run_agent_stream", new_callable=AsyncMock)
+    mock_run_agent_stream.side_effect = Exception("Test error")
+
+    response = runtime_client.post(
+        "/agent/run",
+        json={
+            "agent_id": 1,
+            "conversation_id": 123,
+            "query": "test query",
+            "history": [],
+            "minio_files": [],
+            "is_debug": True,  # Debug mode
+        },
+        headers=mock_auth_header
+    )
+
+    assert response.status_code == 500
+    # In debug mode, actual error should be exposed
+    assert "Test error" in response.json()["detail"]
+
+
+async def test_agent_run_api_error_normal_mode(mocker, mock_auth_header):
+    """Test agent_run_api error case in normal mode - should show generic error."""
+    mock_run_agent_stream = mocker.patch(
+        "apps.agent_app.run_agent_stream", new_callable=AsyncMock)
+    mock_run_agent_stream.side_effect = Exception("Test internal error")
+
+    response = runtime_client.post(
+        "/agent/run",
+        json={
+            "agent_id": 1,
+            "conversation_id": 123,
+            "query": "test query",
+            "history": [],
+            "minio_files": [],
+            "is_debug": False,  # Normal mode
+        },
+        headers=mock_auth_header
+    )
+
+    assert response.status_code == 500
+    # In normal mode, generic error message should be shown
+    assert response.json()["detail"] == "Agent run error."
+    # Actual error should NOT be exposed in normal mode
+    assert "Test internal error" not in response.json()["detail"]
+
+
 def test_agent_run_api_exception(mocker, mock_auth_header):
     """Test agent_run_api exception handling."""
     mock_run_agent_stream = mocker.patch(