fastapi

name: fastapi description: FastAPI framework best practices including Pydantic schemas, dependency injection, and async patterns. globs: ["/main.py", "/routers//*.py", "/schemas/**/*.py"] priority: 90 tags: ["framework"]

FastAPI Best Practices

Project Structure

• app/main.py - Application entry
• app/routers/ - Route handlers
• app/models/ - SQLAlchemy models
• app/schemas/ - Pydantic schemas
• app/services/ - Business logic
• app/dependencies.py - Dependency injection

Pydantic Schemas

• Use separate schemas for input/output
• Use Field() for validation
• Use model_validator for complex validation
• Use Config for schema settings

Dependency Injection

• Use Depends() for dependencies
• Create reusable dependencies
• Use yield for cleanup logic
• Cache expensive dependencies

Async

• Use async def for I/O operations
• Use httpx for async HTTP
• Use databases/SQLAlchemy async
• Avoid blocking in async context

Performance

• Use response_model for serialization
• Enable response caching
• Use background tasks
• Stream large responses
• Use connection pooling