fix(mcp): resolve OpenAPI tool metadata from the local registry before any tools/list

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

litellm/proxy/_experimental/mcp_server/mcp_server_manager.py

@@ -127,6 +127,7 @@ from litellm.proxy._experimental.mcp_server.outbound_credentials.types import (
 from litellm.proxy._experimental.mcp_server.sampling_handler import (
     MCP_SAMPLING_AVAILABLE,
 )
+from litellm.proxy._experimental.mcp_server.tool_registry import global_mcp_tool_registry
 from litellm.proxy._experimental.mcp_server.utils import (
     MCP_TOOL_PREFIX_SEPARATOR,
     MCPMissingUserEnvVarsError,
@@ -4242,9 +4243,11 @@ class MCPServerManager:
                 # applied (e.g. "test_petstore-getinventory").  Do NOT pass them
                 # through _create_prefixed_tools — that would add the prefix a second
                 # time producing "test_petstore-test_petstore-getinventory".
+                if add_prefix:
+                    return tools
                 prefix: Final = get_server_prefix(server)
                 sep: Final = MCP_TOOL_PREFIX_SEPARATOR
-                bare_tools: Final = [  # mutable-ok: returned through the list[MCPTool] listing contract
+                return [  # mutable-ok: returned through the list[MCPTool] listing contract
                     (
                         t.model_copy(update={"name": t.name[len(prefix) + len(sep) :]})
                         if t.name.startswith(f"{prefix}{sep}")
@@ -4252,8 +4255,6 @@ class MCPServerManager:
                     )
                     for t in tools
                 ]
-                self._listed_tools_by_server_id[server.server_id] = MappingProxyType({t.name: t for t in bare_tools})
-                return tools if add_prefix else bare_tools
             else:
                 tools = await self._fetch_tools_with_timeout(client, server.name)
                 self._remember_upstream_initialize_instructions(server, client)
@@ -5139,6 +5140,14 @@ class MCPServerManager:
         return prefixed_tools
 
     def get_listed_tool(self, server: MCPServer, name: str) -> MCPTool | None:
+        if server.spec_path:
+            bare_name: Final = strip_known_server_prefix(name, server)
+            registered: Final = global_mcp_tool_registry.get_tool(
+                f"{get_server_prefix(server)}{MCP_TOOL_PREFIX_SEPARATOR}{bare_name}"
+            ) or global_mcp_tool_registry.get_tool(bare_name)
+            if registered is None:
+                return None
+            return MCPTool(name=bare_name, description=registered.description, inputSchema=registered.input_schema)
         listed: Final = self._listed_tools_by_server_id.get(server.server_id)
         if not listed:
             return None

tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server.py

@@ -17,7 +17,6 @@ from mcp.types import (
     TextContent,
     TextResourceContents,
 )
-from mcp.types import Tool as MCPTool
 
 from litellm.proxy._types import (
     LiteLLM_MCPServerTable,
@@ -7161,9 +7160,9 @@ async def test_execute_mcp_tool_sets_model_in_model_call_details():
 
 
 @pytest.mark.asyncio
-async def test_execute_mcp_tool_hands_openapi_listed_tool_metadata_to_pre_call_hooks():
+async def test_execute_mcp_tool_hands_openapi_registered_tool_metadata_to_pre_call_hooks():
     """OpenAPI-generated tools dispatch through the local registry, so the pre-call hooks must get the
-    listed description and input schema on that path too, not only on the managed-server path."""
+    registered description and input schema on that path too, even when no tools/list ran first."""
     from litellm.proxy._experimental.mcp_server import server as mcp_module
 
     petstore = MCPServer(
@@ -7179,9 +7178,7 @@ async def test_execute_mcp_tool_hands_openapi_listed_tool_metadata_to_pre_call_h
         name="petstore-list_pets", description="List the pets", input_schema=schema, handler=lambda: None
     )
     manager = mcp_module.global_mcp_server_manager
-    manager._create_prefixed_tools(
-        [MCPTool(name="list_pets", description="List the pets", inputSchema=schema)], petstore
-    )
+    manager._listed_tools_by_server_id.pop(petstore.server_id, None)
     pre_call_tool_check = AsyncMock(return_value={})
 
     try:
@@ -7206,10 +7203,13 @@ async def test_execute_mcp_tool_hands_openapi_listed_tool_metadata_to_pre_call_h
             )
     finally:
         mcp_module.global_mcp_tool_registry.unregister_tools_with_prefix("petstore-")
-        manager._listed_tools_by_server_id.pop(petstore.server_id, None)
 
     handed_tool = pre_call_tool_check.call_args.kwargs["tool"]
-    assert handed_tool is not None and (handed_tool.description, handed_tool.inputSchema) == ("List the pets", schema)
+    assert (handed_tool.name, handed_tool.description, handed_tool.inputSchema) == (
+        "list_pets",
+        "List the pets",
+        schema,
+    )
 
 
 @pytest.mark.asyncio

tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py

@@ -6504,9 +6504,9 @@ class TestMCPServerManager:
         assert by_prefixed_name is not None and by_prefixed_name.description == "v2"
         assert manager.get_listed_tool(server, "missing") is None
 
-    @pytest.mark.asyncio
-    @pytest.mark.parametrize("add_prefix", [True, False])
-    async def test_openapi_listing_records_tool_metadata_for_pre_call_hooks(self, add_prefix):
+    def test_get_listed_tool_reads_openapi_registry_without_a_prior_listing(self):
+        """OpenAPI tools live in the local registry from registration on, so their metadata must resolve
+        before any tools/list has run and must disappear with the registration."""
         from litellm.proxy._experimental.mcp_server.tool_registry import global_mcp_tool_registry
 
         server = MCPServer(
@@ -6519,19 +6519,21 @@ class TestMCPServerManager:
         )
         schema = {"type": "object", "properties": {"petId": {"type": "integer"}}}
         manager = MCPServerManager()
-        manager._create_mcp_client = AsyncMock(return_value=AsyncMock())
         global_mcp_tool_registry.register_tool(
             name="petstore-get_pet", description="Fetch a pet", input_schema=schema, handler=lambda: None
         )
         try:
-            listed = await manager._get_tools_from_server(server=server, add_prefix=add_prefix)
+            for spelling in ("get_pet", "petstore-get_pet"):
+                tool = manager.get_listed_tool(server, spelling)
+                assert tool is not None and (tool.name, tool.description, tool.inputSchema) == (
+                    "get_pet",
+                    "Fetch a pet",
+                    schema,
+                )
         finally:
             global_mcp_tool_registry.unregister_tools_with_prefix("petstore-")
 
-        assert [t.name for t in listed] == ["petstore-get_pet" if add_prefix else "get_pet"]
-        for spelling in ("get_pet", "petstore-get_pet"):
-            tool = manager.get_listed_tool(server, spelling)
-            assert tool is not None and (tool.description, tool.inputSchema) == ("Fetch a pet", schema)
+        assert manager.get_listed_tool(server, "petstore-get_pet") is None
 
     @pytest.mark.asyncio
     async def test_get_allowed_mcp_servers_with_user_api_key_auth(self):