How to connect MCP tools to LangChain agent

pip install mcp langchain langchain_openai

import os
from mcp.server import Server
from mcp.server.stdio import stdio_server
from langchain.agents.mcp import MCPAgent
from langchain_openai import ChatOpenAI

# Define a simple MCP tool handler
class EchoTool:
    def run(self, input_text: str) -> str:
        return f"Echo: {input_text}"

# Start MCP server exposing the EchoTool
server = Server()
server.add_tool("echo", EchoTool())

# Run the MCP server in a background thread or process (for demo, run in main thread)
import threading
threading.Thread(target=stdio_server, args=(server,), daemon=True).start()

# Setup LangChain MCPAgent to connect to the MCP server
# MCPAgent expects the server to be accessible via stdio or SSE transport

# Initialize OpenAI chat model
chat_model = ChatOpenAI(model="gpt-4o", temperature=0, openai_api_key=os.environ["OPENAI_API_KEY"])

# Create MCPAgent instance
agent = MCPAgent.from_stdio(
    chat=chat_model,
    tool_names=["echo"]
)

# Use the agent to call the MCP tool
response = agent.invoke([{"role": "user", "content": "Hello MCP tool!"}])
print("Agent response:", response.content)