fix(mcp): warn and return empty when native MCP server returns no tools

lib/crewai/src/crewai/mcp/tool_resolver.py

@@ -374,6 +374,7 @@ class MCPToolResolver:
                             "MCP connection failed due to event loop cleanup issues. "
                             "This may be due to authentication errors or server unavailability."
                         ) from e
+                    raise
                 except asyncio.CancelledError as e:
                     raise ConnectionError(
                         "MCP connection was cancelled. This may indicate an authentication "
@@ -401,6 +402,13 @@ class MCPToolResolver:
                         filtered_tools.append(tool)
                 tools_list = filtered_tools
 
+            if not tools_list:
+                self._logger.log(
+                    "warning",
+                    f"No tools discovered from MCP server: {server_name}",
+                )
+                return cast(list[BaseTool], []), []
+
             def _client_factory() -> MCPClient:
                 transport, _ = self._create_transport(mcp_config)
                 return MCPClient(

lib/crewai/tests/mcp/test_tool_resolver_native.py

@@ -0,0 +1,99 @@
+"""Tests for MCPToolResolver native (non-AMP) resolution paths."""
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+from crewai.agent.core import Agent
+from crewai.mcp.config import MCPServerHTTP
+from crewai.mcp.tool_resolver import MCPToolResolver
+
+
+@pytest.fixture
+def agent():
+    return Agent(
+        role="Test Agent",
+        goal="Test goal",
+        backstory="Test backstory",
+    )
+
+
+@pytest.fixture
+def resolver(agent):
+    return MCPToolResolver(agent=agent, logger=agent._logger)
+
+
+@pytest.fixture
+def http_config():
+    return MCPServerHTTP(url="https://mcp.example.com/api")
+
+
+class TestResolveNativeEmptyTools:
+    @patch("crewai.mcp.tool_resolver.MCPClient")
+    def test_logs_warning_and_returns_empty_when_server_has_no_tools(
+        self, mock_client_class, resolver, http_config
+    ):
+        mock_client = AsyncMock()
+        mock_client.list_tools = AsyncMock(return_value=[])
+        mock_client.connected = False
+        mock_client.connect = AsyncMock()
+        mock_client.disconnect = AsyncMock()
+        mock_client_class.return_value = mock_client
+
+        mock_log = MagicMock()
+        resolver._logger = MagicMock(log=mock_log)
+
+        tools, clients = resolver._resolve_native(http_config)
+
+        assert tools == []
+        assert clients == []
+        warning_calls = [
+            call for call in mock_log.call_args_list if call.args[0] == "warning"
+        ]
+        assert any(
+            "No tools discovered from MCP server" in call.args[1]
+            for call in warning_calls
+        )
+
+    @patch("crewai.mcp.tool_resolver.MCPClient")
+    def test_logs_warning_when_tool_filter_removes_all_tools(
+        self, mock_client_class, resolver
+    ):
+        mock_client = AsyncMock()
+        mock_client.list_tools = AsyncMock(
+            return_value=[{"name": "search", "description": "Search"}]
+        )
+        mock_client.connected = False
+        mock_client.connect = AsyncMock()
+        mock_client.disconnect = AsyncMock()
+        mock_client_class.return_value = mock_client
+
+        config = MCPServerHTTP(
+            url="https://mcp.example.com/api",
+            tool_filter=lambda _tool: False,
+        )
+
+        mock_log = MagicMock()
+        resolver._logger = MagicMock(log=mock_log)
+
+        tools, clients = resolver._resolve_native(config)
+
+        assert tools == []
+        assert clients == []
+        warning_calls = [
+            call for call in mock_log.call_args_list if call.args[0] == "warning"
+        ]
+        assert any(
+            "No tools discovered from MCP server" in call.args[1]
+            for call in warning_calls
+        )
+
+
+class TestResolveNativeRuntimeError:
+    @patch("crewai.mcp.tool_resolver.asyncio.run")
+    def test_unmatched_runtime_error_is_wrapped_not_swallowed(
+        self, mock_asyncio_run, resolver, http_config
+    ):
+        mock_asyncio_run.side_effect = RuntimeError("some other failure")
+
+        with pytest.raises(RuntimeError, match="Failed to get native MCP tools"):
+            resolver._resolve_native(http_config)