MCP package dependency check (#561)

* MCP package dependency check.

- Added a runtime check for the "fastmcp" package in `mcp.py`, raising an error if it is not installed.
- Updated the error message to provide clearer installation instructions.

* fix

* apply suggestin

* update requirement

Author: aniketmaurya

_requirements/test.txt

@@ -15,4 +15,4 @@ openai>=1.12.0
 pillow
 numpy <3.0
 pytest-retry>=1.6.3
-mcp>=1.9.2; python_version >= '3.10'
+fastmcp>=2.9.2; python_version >= '3.10'

src/litserve/mcp.py

@@ -20,18 +20,27 @@
 from contextlib import asynccontextmanager
 from typing import TYPE_CHECKING, Any, Dict, List, Optional, Union, get_args, get_origin
 
-import mcp.types as types
 from fastapi import FastAPI
-from mcp.server.fastmcp.server import _convert_to_content
-from mcp.server.lowlevel import Server as MCPServer
-from mcp.server.streamable_http_manager import StreamableHTTPSessionManager
 from pydantic import BaseModel
 from starlette.applications import Starlette
 from starlette.routing import Mount
 from starlette.types import Receive, Scope, Send
 
 from litserve.utils import is_package_installed
 
+_is_mcp_installed = is_package_installed("fastmcp")
+
+
+if _is_mcp_installed:
+    from fastapi import FastAPI
+    from mcp.server.fastmcp.server import _convert_to_content
+    from mcp.server.lowlevel import Server as MCPServer
+    from mcp.server.streamable_http_manager import StreamableHTTPSessionManager
+    from mcp.types import Tool as ToolType
+
+else:
+    ToolType = object
+
 if TYPE_CHECKING:
     from litserve.api import LitAPI
 
@@ -243,7 +252,7 @@ async def _call_handler(handler, **kwargs):
     return _convert_to_content(await handler(*bound.args, **bound.kwargs))
 
 
-class ToolEndpointType(types.Tool):
+class ToolEndpointType(ToolType):
     endpoint: str
 
 
@@ -348,6 +357,11 @@ def __init__(
         self.input_schema = input_schema
         self._connected = False
 
+        if not is_package_installed("fastmcp"):
+            raise RuntimeError(
+                "mcp package is required for MCP support. To install, run `pip install fastmcp` in the terminal."
+            )
+
     @property
     def name(self) -> str:
         return self._name
@@ -364,11 +378,6 @@ def _connect(self, lit_api: "LitAPI"):
         self._connected = True
 
     def as_tool(self) -> ToolEndpointType:
-        if not is_package_installed("mcp"):
-            raise RuntimeError(
-                "MCP is not installed. Please install it with `pip install mcp[cli]` or `uv pip install mcp[cli]`"
-            )
-
         if not self._connected:
             raise RuntimeError("MCP is not connected to a LitAPI.")
 
@@ -400,7 +409,7 @@ def as_tool(self) -> ToolEndpointType:
 
 
 class _MCPRequestHandler:
-    def __init__(self, mcp_server: MCPServer):
+    def __init__(self, mcp_server: "MCPServer"):
         self.mcp_server = mcp_server
         self._session_manager = None
 
@@ -536,7 +545,7 @@ async def _call_tool(name: str, arguments: dict):
         starlette_app = self.request_handler.streamable_http_app()
         app.mount("/", starlette_app, name="mcp")
 
-    def connect_mcp_server(self, mcp_tools: List[types.Tool], app: FastAPI):
+    def connect_mcp_server(self, mcp_tools: List[ToolType], app: FastAPI):
         """LitServer calls this method to connect MCP server to the FastAPI app.
 
         Args:

tests/unit/test_mcp.py

@@ -1,6 +1,7 @@
 import inspect
 import sys
 from typing import Dict, List, Optional
+from unittest.mock import patch
 
 import pytest
 from fastapi import FastAPI
@@ -20,6 +21,15 @@
 )
 
 
+@patch("litserve.mcp.is_package_installed", return_value=False)
+def test_mcp_not_installed(mock_is_package_installed):
+    with pytest.raises(
+        RuntimeError,
+        match="mcp package is required for MCP support. To install, run `pip install fastmcp` in the terminal.",
+    ):
+        MCP()
+
+
 def test_python_type_to_json_schema():
     assert _python_type_to_json_schema(inspect.Parameter.empty) == "string"
     assert _python_type_to_json_schema(int) == "integer"