MCP Integration

Model Context Protocol (MCP) is an open protocol that standardizes how applications provide tools and context to language models. LangGraph agents can use tools defined on MCP servers through the @langchain/mcp-adapters library.

Install the @langchain/mcp-adapters library to use MCP tools in LangGraph:

npm install @langchain/mcp-adapters

Use MCP tools

The @langchain/mcp-adapters package enables agents to use tools defined across one or more MCP servers.

// highlight-next-line
import { MultiServerMCPClient } from "@langchain/mcp-adapters";
import { initChatModel } from "langchain/chat_models/universal";
import { createReactAgent } from "@langchain/langgraph/prebuilt";

// highlight-next-line
const client = new MultiServerMCPClient({
  mcpServers: {
    "math": {
      command: "python",
      // Replace with absolute path to your math_server.py file
      args: ["/path/to/math_server.py"],
      transport: "stdio",
    },
    "weather": {
      // Ensure your start your weather server on port 8000
      url: "http://localhost:8000/sse",
      transport: "sse",
    }
  }
})

const llm = await initChatModel("anthropic:claude-3-7-sonnet-latest");
const agent = createReactAgent({
  llm,
  // highlight-next-line
  tools: await client.getTools()
});
 
const mathResponse = await agent.invoke(
  { messages: [ { role: "user", content: "what's (3 + 5) x 12?" } ] }
);
const weatherResponse = await agent.invoke(
  { messages: [ { role: "user", content: "what is the weather in nyc?" } ] }
);
await client.close();

Custom MCP servers

To create your own MCP servers, you can use the mcp library in Python (or @modelcontextprotocol/sdk in TypeScript). These libraries provide a simple way to define tools and run them as servers.

Install the MCP library:

pip install mcp

Use the following reference implementations to test your agent with MCP tool servers.

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("Math")

@mcp.tool()
def add(a: int, b: int) -> int:
    """Add two numbers"""
    return a + b

@mcp.tool()
def multiply(a: int, b: int) -> int:
    """Multiply two numbers"""
    return a * b

if __name__ == "__main__":
    mcp.run(transport="stdio")

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("Weather")

@mcp.tool()
async def get_weather(location: str) -> str:
    """Get weather for location."""
    return "It's always sunny in New York"

if __name__ == "__main__":
    mcp.run(transport="sse")

Additional resources

• MCP documentation
• MCP Transport documentation