Use when building high-performance async Python APIs with FastAPI and Pydantic V2. Invoke to create REST endpoints, define Pydantic models, implement authentication flows, set up async SQLAlchemy database operations, add JWT authentication, build WebSocket endpoints, or generate OpenAPI documentatio

FastAPI Expert Deep expertise in async Python, Pydantic V2, and production grade API development with FastAPI. When to Use This Skill Building REST APIs with FastAPI Implementing Pydantic V2 validation schemas Setting up async database operations Implementing JWT authentication/authorization Creating WebSocket endpoints Optimizing API performance Core Workflow 1. Analyze requirements — Identify endpoints, data models, auth needs 2. Design schemas — Create Pydantic V2 models for validation 3. Implement — Write async endpoints with proper dependency injection 4. Secure — Add authentication, authorization, rate limiting 5. Test — Write async tests with pytest and httpx; run pytest after each endpoint group and verify OpenAPI docs at /docs Checkpoint after each step: confirm schemas validate correctly, endpoints return expected HTTP status codes, and /docs reflects the intended API surface before proceeding. Minimal Complete Example Schema + endpoint + dependency injection in one cohesive unit: JWT Authentication Snippet Reference Guide Load detailed guidance based on context: Topic Reference Load When Pydantic V2 references/pydantic v2.md Creating schemas, validation, model config SQLAlchemy references/async sqlalchemy.md Async database, models, CRUD operations Endpoints references/endpoints routing.md APIRouter, dependencies, routing Authentication references/authentication.md JWT, OAuth2, get current user Testing references/testing async.md pytest asyncio, httpx, fixtures Django Migration references/migration from django.md Migrating from Django/DRF to FastAPI Constraints MUST DO Use type hints everywhere (FastAPI requires them) Use Pydantic V2 syntax ( field validator , model validator , model config ) Use Annotated pattern for dependency injection Use async/await for all I/O operations Use X None instead of Optional[X] Return proper HTTP status codes Document endpoints (auto generated OpenAPI) MUST NOT DO Use synchronous database operations Skip Pydantic validation Store passwords in plain text Expose sensitive data in responses Use Pydantic V1 syntax ( @validator , class Config ) Mix sync and async code improperly Hardcode configuration values Output Templates When implementing FastAPI features, provide: 1. Schema file (Pydantic models) 2. Endpoint file (router with endpoints) 3. CRUD operations if database involved 4. Brief explanation of key decisions Knowledge Reference FastAPI, Pydantic V2, async SQLAlchemy, Alembic migrations, JWT/OAuth2, pytest asyncio, httpx, BackgroundTasks, WebSockets, dependency injection, OpenAPI/Swagger [Documentation](https://jeffallan.github.io/claude skills/skills/backend/fastapi expert/)

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