Tools — giving the agent hands

In one line

A tool is a function the model can call. Its docstring tells the model when to use it.

Key idea

Use @tool for your own logic. Use MCP to plug into outside services. Mix both in one list.

from langchain.tools import tool
@tool
def get_weather(city: str) -> str:
    """Get the current weather for a city."""
    return f"sunny and 70F in {city}"

MCP — borrow tools from anywhere

• langchain-mcp-adapters turns MCP tools into LangChain tools.
• MultiServerMCPClient connects to many servers; get_tools() loads them.
• Transports: stdio and streamable_http.

Links

• MCP docs
• langchain-mcp-adapters
• Full guide — appendix F (MCP)

My notes