Agent skill · affaan-m
fastapi-patterns
FastAPI best practices covering project structure, Pydantic v2 schemas, dependency injection, async handlers, authentication, authorization, transactional service layers, and testing with httpx and pytest. Use when building or reviewing FastAPI apps — Pydantic schemas, dependencies, async handlers, auth, or tests.
What it needs
About 6k tokens when loaded.
What this skill does
FastAPI Patterns Modern, production-grade FastAPI development: project layout, Pydantic v2 schemas, dependency injection, async patterns, auth, transactional service methods, and testing. Project Structure --- App Factory and Lifespan --- Configuration with pydantic-settings --- Pydantic Schemas (v2) --- Dependency Injection --- Router and Endpoint Design --- Service Layer Note on Database Design: Application-level unique handling requires an underlying unique database index (e.g., unique=True on your SQLAlchemy mapping attributes). Without underlying constraints, application layer error-catching cannot safely prevent concurrent race conditions. --- Testing with httpx and pytest --- Anti-Patterns --- Best Practices Always declare a typed responsemodel to prevent accidental PII/data leaks and output clean OpenAPI schemas. Consolidate standard middleware dependency injections via type-aliasing: DbDep = Annotated[AsyncSession, Depends(getdb)]. Wrap database mutation boundaries gracefully within transactions inside your service layer, catching structural database errors directly. Parse JWT parameters defensively, expecting potential string/integer cast mismatches from modern payload variations. Enforce deterministic sorting (e.g., .orderby(Model.id)) on all offset/limit paginated endpoints to avoid data skips. Isolate authorization checks from core authentication dependencies to provide precise REST status signals (401 vs 403).
How to use it
Reference it in AdaL, Claude Code, Cursor or any coding agent — nothing to install:
@skills affaan-m/fastapi-patterns--7670ff