MCP Patterns
Model Context Protocol (MCP) server patterns for building integrations with Claude Code.
Basic MCP Server (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.mdClaude Desktop Configuration
Basic Configuration
{
"mcpServers": {
"my-server": {
"command": "python",
"args": ["-m", "my_server"],
"env": {
"MY_API_KEY": "your-key-here"
}
}
}
}With uv (Recommended)
{
"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