Practical MCP with FastMCP & LangChain

Creating Your First FastMCP Server

Now that we have FastMCP installed, we can create our first server. This is how we instantiate a FastMCP server:

from fastmcp import FastMCP

mcp = FastMCP("My MCP Server")

To add a tool, we simply define a Python function and decorate it with @mcp.tool. For example:

@mcp.tool
def sum(a: int, b: int) -> int:
    """Returns the sum of two numbers."""
    return a + b

This defines a tool called sum that takes two integers as input and returns their sum. The @mcp.tool decorator registers this function as a tool that can be called by clients.

Now, depending on the transport we want to use, we can start the server with different configurations.

For HTTP, we can run:

if __name__ == "__main__":
    mcp.run(transport="http", host="localhost", port=8000)

For STDIO, we can run: