from collections.abc import Sequence

from typing import Any

from mcp import Client

from mcp.server.extension import Extension, ToolBinding

from mcp.server.mcpserver import MCPServer

def stamp(text: str) -> str:

"""Stamp a message with the office seal."""

return f"[stamped] {text}"

class Stamps(Extension):

"""A purely additive extension: one tool, one capability entry."""

identifier = "com.example/stamps"

def settings(self) -> dict[str, Any]:

return {"sealed": True}

def tools(self) -> Sequence[ToolBinding]:

return [ToolBinding(fn=stamp)]

mcp = MCPServer("post-office", extensions=[Stamps()])

async def main() -> None:

async with Client(mcp) as client:

print(client.server_capabilities.extensions)

# {'com.example/stamps': {'sealed': True}}

result = await client.call_tool("stamp", {"text": "hello"})

print(result.content)

# [TextContent(text='[stamped] hello')]