MCP Patterns

Model Context Protocol (MCP) server patterns for building integrations with Claude Code.

Basic MCP Server (Python)

python
from mcp.server import Server
from mcp.server.stdio import stdio_server

app = Server("my-server")

@app.list_tools()
async def list_tools():
    return [
        {
            "name": "my_tool",
            "description": "Does something useful",
            "inputSchema": {
                "type": "object",
                "properties": {
                    "query": {"type": "string", "description": "Search query"}
                },
                "required": ["query"]
            }
        }
    ]

@app.call_tool()
async def call_tool(name: str, arguments: dict):
    if name == "my_tool":
        result = await do_something(arguments["query"])
        return {"content": [{"type": "text", "text": result}]}
    raise ValueError(f"Unknown tool: {name}")

async def main():
    async with stdio_server() as (read_stream, write_stream):
        await app.run(read_stream, write_stream, app.create_initialization_options())

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

Project Layout

my-mcp-server/
├── src/
│   └── my_server/
│       ├── __init__.py
│       ├── server.py       # Main server logic
│       ├── tools.py        # Tool handlers
│       └── resources.py    # Resource handlers
├── pyproject.toml
└── README.md

Claude Desktop Configuration

Basic Configuration

json
{
  "mcpServers": {
    "my-server": {
      "command": "python",
      "args": ["-m", "my_server"],
      "env": {
        "MY_API_KEY": "your-key-here"
      }
    }
  }
}

With uv (Recommended)

json
{
  "mcpServers": {
    "my-server": {
      "command": "uv",
      "args": ["run", "--directory", "/path/to/my-server", "python", "-m", "my_server"],
      "env": {
        "MY_API_KEY": "your-key-here"
      }
    }
  }
}

Quick Reference

| Pattern | Use Case | Reference | |---------|----------|-----------| | Tool validation | Input sanitization with Pydantic | ./references/tool-patterns.md | | Error handling | Graceful failure responses | ./references/tool-patterns.md | | Multiple tools | CRUD-style tool registration | ./references/tool-patterns.md | | Static resources | Config/settings exposure | ./references/resource-patterns.md | | Dynamic resources | Database-backed resources | ./references/resource-patterns.md | | Environment auth | API key from env vars | ./references/auth-patterns.md | | OAuth tokens | Token refresh with TTL | ./references/auth-patterns.md | | SQLite cache | Persistent state storage | ./references/state-patterns.md | | In-memory cache | TTL-based caching | ./references/state-patterns.md | | Manual testing | Quick validation script | ./references/testing-patterns.md | | pytest async | Unit tests for tools | ./references/testing-patterns.md |

Common Issues

| Issue | Solution | |-------|----------| | Server not starting | Check command path, ensure dependencies installed | | Tool not appearing | Verify list_tools() returns valid schema | | Auth failures | Check env vars are set in config, not shell | | Timeout errors | Add timeout to httpx calls, use async properly | | JSON parse errors | Ensure call_tool returns proper content structure |

Official Documentation

• https://modelcontextprotocol.io - MCP specification
• https://modelcontextprotocol.io/docs/concepts/tools - Tools reference
• https://modelcontextprotocol.io/docs/concepts/resources - Resources reference
• https://github.com/modelcontextprotocol/python-sdk - Python SDK
• https://github.com/modelcontextprotocol/servers - Official MCP servers

Additional Resources

For detailed patterns, load:

• ./references/tool-patterns.md - Validation, error handling, multi-tool registration
• ./references/resource-patterns.md - Static and dynamic resource exposure
• ./references/auth-patterns.md - Environment variables, OAuth token refresh
• ./references/state-patterns.md - SQLite persistence, in-memory caching
• ./references/testing-patterns.md - Manual test scripts, pytest async patterns