fix mcp tools list parsing

litellm/experimental_mcp_client/client.py

@@ -86,6 +86,10 @@ class _LenientListPromptsResult(types.ListPromptsResult):
     prompts: List[Prompt] = Field(default_factory=list)
 
 
+class _LenientListToolsResult(types.ListToolsResult):
+    tools: List[MCPTool] = Field(default_factory=list)
+
+
 class _LenientListResourcesResult(types.ListResourcesResult):
     resources: List[Resource] = Field(default_factory=list)
 
@@ -521,7 +525,10 @@ class MCPClient:
         )
 
         async def _list_tools_operation(session: ClientSession):
-            return await session.list_tools()
+            return await session.send_request(
+                types.ClientRequest(types.ListToolsRequest(params=None)),
+                _LenientListToolsResult,
+            )
 
         try:
             result = await self.run_with_session(_list_tools_operation)

tests/test_litellm/experimental_mcp_client/test_mcp_client.py

@@ -425,6 +425,53 @@ class TestMCPClientInstructionsCapture:
         assert client._last_initialize_instructions is None
 
 
+# ---------------------------------------------------------------------------
+# MCP list result tolerance
+# ---------------------------------------------------------------------------
+
+
+class TestMCPListOperations:
+    """MCP list operations should tolerate omitted empty list fields."""
+
+    async def _run_list_operation(self, method_name, result_type):
+        client = MCPClient(server_url="http://example.com/mcp", transport_type="http")
+        session = AsyncMock()
+
+        async def send_request(_request, actual_result_type):
+            assert actual_result_type is result_type
+            return actual_result_type.model_validate({})
+
+        session.send_request = AsyncMock(side_effect=send_request)
+
+        async def run_with_session(operation):
+            return await operation(session)
+
+        client.run_with_session = AsyncMock(side_effect=run_with_session)
+
+        result = await getattr(client, method_name)()
+
+        assert result == []
+        session.send_request.assert_awaited_once()
+
+    @pytest.mark.asyncio
+    async def test_list_tools_tolerates_missing_tools_field(self):
+        await self._run_list_operation(
+            "list_tools", mcp_client_module._LenientListToolsResult
+        )
+
+    @pytest.mark.asyncio
+    async def test_list_resources_tolerates_missing_resources_field(self):
+        await self._run_list_operation(
+            "list_resources", mcp_client_module._LenientListResourcesResult
+        )
+
+    @pytest.mark.asyncio
+    async def test_list_prompts_tolerates_missing_prompts_field(self):
+        await self._run_list_operation(
+            "list_prompts", mcp_client_module._LenientListPromptsResult
+        )
+
+
 # ---------------------------------------------------------------------------
 # Transport error surfacing
 # ---------------------------------------------------------------------------
@@ -542,44 +589,6 @@ class TestExecuteSessionOperationSurfacesTransportError:
         result = await client._execute_session_operation(transport_ctx, _op)
         assert result == "done"
 
-    @pytest.mark.asyncio
-    async def test_list_resources_tolerates_missing_resources_field(self):
-        client = MCPClient(server_url="http://example.com/mcp", transport_type="http")
-        session = AsyncMock()
-
-        async def send_request(_request, result_type):
-            assert result_type is mcp_client_module._LenientListResourcesResult
-            return result_type.model_validate({})
-
-        session.send_request = AsyncMock(side_effect=send_request)
-
-        async def run_with_session(operation):
-            return await operation(session)
-
-        client.run_with_session = AsyncMock(side_effect=run_with_session)
-
-        assert await client.list_resources() == []
-        session.send_request.assert_awaited_once()
-
-    @pytest.mark.asyncio
-    async def test_list_prompts_tolerates_missing_prompts_field(self):
-        client = MCPClient(server_url="http://example.com/mcp", transport_type="http")
-        session = AsyncMock()
-
-        async def send_request(_request, result_type):
-            assert result_type is mcp_client_module._LenientListPromptsResult
-            return result_type.model_validate({})
-
-        session.send_request = AsyncMock(side_effect=send_request)
-
-        async def run_with_session(operation):
-            return await operation(session)
-
-        client.run_with_session = AsyncMock(side_effect=run_with_session)
-
-        assert await client.list_prompts() == []
-        session.send_request.assert_awaited_once()
-
 
 if __name__ == "__main__":
     pytest.main([__file__])