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.

Author: aniketmaurya

src/litserve/mcp.py

@@ -20,18 +20,24 @@
 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
 
+if not is_package_installed("fastmcp"):
+    raise RuntimeError(
+        "mcp package is required for MCP support. To install, run `pip install fastmcp` in the terminal."
+    )
+
+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
+
 if TYPE_CHECKING:
     from litserve.api import LitAPI
 
@@ -364,9 +370,9 @@ def _connect(self, lit_api: "LitAPI"):
         self._connected = True
 
     def as_tool(self) -> ToolEndpointType:
-        if not is_package_installed("mcp"):
+        if not is_package_installed("fastmcp"):
             raise RuntimeError(
-                "MCP is not installed. Please install it with `pip install mcp[cli]` or `uv pip install mcp[cli]`"
+                "fastmcp package is required for MCP support. To install, run `pip install fastmcp` in the terminal."
             )
 
         if not self._connected:

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 +21,16 @@
 )
 
 
+@patch("litserve.mcp.is_package_installed", return_value=False)
+def test_mcp_not_installed(mock_is_package_installed):
+    with pytest.raises(
+        RuntimeError,
+        match="fastmcp package is required for MCP support. To install, run `pip install fastmcp` in the terminal.",
+    ):
+        MCP().as_tool()
+    mock_is_package_installed.assert_called_once_with("fastmcp")
+
+
 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"