backend-dev-guidelines

Comprehensive backend development guide for Python/FastAPI/SQLAlchemy applications. Use when creating routes, services, models, schemas, database operations, or working with FastAPI endpoints, SQLAlchemy/Alembic migrations, Pydantic validation, error handling, dependency injection, or async patterns. Covers layered architecture (routes → services → repositories → models), separation of concerns, error handling, performance, testing strategies, and best practices.