The MCP Python SDK: Building clients and servers

uv init mcp-python-demo
cd mcp-python-demo
uv add "mcp[cli]"

pip install "mcp[cli]"

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("calculator-server")


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


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

uv run python server.py

@mcp.resource("greeting://{name}")
def greeting(name: str) -> str:
    """Return a personalized greeting."""
    return f"Hello, {name}!"

@mcp.prompt()
def review_code(code: str) -> str:
    """Prepare a focused code-review request."""
    return (
        "Review this code for correctness, security, and maintainability:\n\n"
        f"{code}"
    )

import asyncio

from mcp import ClientSession, StdioServerParameters
from mcp.client.stdio import stdio_client


async def main() -> None:
    server = StdioServerParameters(
        command="uv",
        args=["run", "python", "server.py"],
    )

    async with stdio_client(server) as (read, write):
        async with ClientSession(read, write) as session:
            await session.initialize()

            tools = await session.list_tools()
            print([tool.name for tool in tools.tools])

            result = await session.call_tool(
                "add",
                arguments={"a": 2, "b": 3},
            )
            print(result)


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

from mcp.server.fastmcp import Context


@mcp.tool()
async def process_report(report_id: str, ctx: Context) -> str:
    """Process a report and send progress updates."""
    await ctx.info(f"Starting report {report_id}")
    await ctx.report_progress(progress=0.5, total=1.0)

    result = await process_report_in_backend(report_id)

    await ctx.report_progress(progress=1.0, total=1.0)
    return result

app/
  server.py
  tools/
    orders.py
    customers.py
  resources/
    policies.py
  prompts/
    support.py
  services/
    api_client.py
tests/

npx @modelcontextprotocol/inspector uv run python server.py