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What is an MCP Server?

An MCP Server exposes tools, resources, and prompts that AI agents can use through the Model Context Protocol. mcp-use provides a simple decorator-based API for creating production-ready MCP servers in Python.

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Key Features

Simple Decorators

Define tools, resources, and prompts with intuitive decorators

Multiple Transports

Support for stdio, SSE, and streamable HTTP

Built-in Inspector

Debug mode with web UI for testing tools

Type Safety

Full type hints and Pydantic validation

Authentication

Built-in bearer token auth support

Middleware

Extensible middleware system

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Quick Example

from mcp_use import MCPServer
from pydantic import Field
from typing import Annotated

server = MCPServer(
    name="my-server",
    version="1.0.0",
    instructions="A simple MCP server example"
)

@server.tool()
def get_weather(city: Annotated[str, Field(description="City name")]) -> dict:
    """Get weather for a city"""
    return {
        "temperature": 72,
        "condition": "sunny",
        "city": city
    }

if __name__ == "__main__":
    server.run()

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Architecture

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Core Concepts

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Tools

Tools are functions that AI agents can call to perform actions: 
@server.tool(
    name="search",
    description="Search for information"
)
async def search(query: str) -> str:
    return f"Results for: {query}"

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Resources

Resources provide read-only data that agents can access: 
@server.resource(
    uri="data://users",
    name="users",
    description="List of users"
)
async def get_users() -> str:
    return json.dumps([{"id": 1, "name": "Alice"}])

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Prompts

Prompts are reusable templates for agent interactions: 
@server.prompt(
    name="greeting",
    description="Personalized greeting"
)
async def greeting(name: str) -> str:
    return f"Hello, {name}! How can I help you today?"

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Transport Modes

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Stdio Transport

For command-line integration and local development: 
server.run(transport="stdio")

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HTTP Transport

For web-based integrations with server-sent events: 
server.run(
    transport="streamable-http",
    host="0.0.0.0",
    port=8000
)

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Debug Mode

Enable debug mode to access development tools: 
server = MCPServer(
    name="my-server",
    debug=True  # Enables /docs, /inspector, /openmcp.json
)

server.run(port=8000)
Debug endpoints:
  • http://localhost:8000/docs - API documentation
  • http://localhost:8000/inspector - Interactive tool testing UI
  • http://localhost:8000/openmcp.json - OpenMCP metadata

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Context Access

Access request context in your tools: 
from mcp.server.fastmcp import Context

@server.tool()
async def get_session_info(context: Context) -> dict:
    """Access session and request information"""
    return {
        "session_id": context.request_context.session_id,
        "capabilities": context.request_context.capabilities
    }

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Error Handling

Return structured errors from tools: 
@server.tool()
async def divide(a: float, b: float) -> float:
    """Divide two numbers"""
    if b == 0:
        raise ValueError("Cannot divide by zero")
    return a / b

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Next Steps

Creating Servers

Learn to build MCP servers

Tools

Define server tools

Resources

Expose data resources

Transport

Configure transport protocols

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