Gavin Wiggins

LangChain MCP Client without LSP Warnings

Published on April 25, 2026

The LangChain documentation gives an example of using multiple MCP servers with an agent by defining a MultiServerMCPClient (see below). The example defines the MCP connections as a dictionary to the MultiServerMCPClient but this triggers LSP warnings about invalid argument types.

client = MultiServerMCPClient(
    {
        "math": {
            "transport": "stdio",
            "command": "python",
            "args": ["/path/to/math_server.py"],
        },
        "weather": {
            "transport": "http",
            "url": "http://localhost:8000/mcp",
        }
    }
)

To fix the LSP warnings, you can define the connections explicitly then pass them to the MultiServerMCPClient as shown below.

import asyncio

from langchain_mcp_adapters.client import MultiServerMCPClient
from langchain_mcp_adapters.sessions import StreamableHttpConnection, StdioConnection
from langchain.agents import create_agent


async def main():
    http_conn: StreamableHttpConnection = {
        "transport": "streamable_http",
        "url": "http://localhost:8000/mcp",
    }

    stdio_conn: StdioConnection = {
        "transport": "stdio",
        "command": "python",
        "args": ["path/to/math_server.py"],
    }

    client = MultiServerMCPClient({"math": stdio_conn, "weather": http_conn})

    tools = await client.get_tools()
    agent = create_agent("claude-sonnet-4-6", tools)

    math_response = await agent.ainvoke(
        {"messages": [{"role": "user", "content": "what's (3 + 5) x 12?"}]}
    )

    weather_response = await agent.ainvoke(
        {"messages": [{"role": "user", "content": "what is the weather in nyc?"}]}
    )

    print(math_response)
    print(weather_response)


if __name__ == "__main__":
    asyncio.run(main())