# Python Fastapi > FastAPI standards for async endpoints, Pydantic models, dependency injection, APIRouter, OpenAPI docs, and background tasks Use when this capability is needed. - Skill: `tomevault-io/python-fastapi-2` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/python-fastapi-2` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/python-fastapi-2/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/python-fastapi-2 --- Full standards in [python-fastapi.md](python-fastapi.md). Always-on summary: **Routing and structure:** - Use `APIRouter` with `prefix="/users"` (explicit `prefix=`) and `tags`; mount routers in `main.py` with `app.include_router()` - Return typed response models via `response_model=` — never return raw dicts from endpoints - Use `status_code=status.HTTP_201_CREATED` (or appropriate) on every route decorator **Pydantic models:** - Separate `CreateSchema`, `UpdateSchema`, and `ReadSchema`; never expose ORM models directly - Use `model_config = ConfigDict(from_attributes=True)` for ORM serialization - Validate at the boundary — put business logic in services, not schemas **Dependency injection:** - Inject DB sessions via `Depends(get_db)` — never create sessions inside route functions - Use `Annotated[T, Depends(fn)]` syntax (FastAPI 0.95+) for cleaner signatures - Raise `HTTPException` in dependencies; FastAPI propagates them automatically **Async:** - Use `async def` for all I/O-bound endpoints; use `def` for CPU-bound work (runs in threadpool) - Never call blocking I/O (requests, psycopg2, etc.) from `async def` — use async drivers **OpenAPI and error handling:** - Add `summary=`, `description=`, and `responses=` to all public endpoints - Define a global exception handler for unhandled errors; return `{"detail": ...}` envelopes **Never:** - Never import `app` directly in sub-modules — use `APIRouter` and mount - Never use `Optional[X]` without a default; prefer `X | None = None` (Python 3.10+) - Never block the event loop with synchronous sleeps — use `await asyncio.sleep()` **Related skills:** error-handling, logging-standards, database-sql, api-conventions --- > Source: [manikumarkv/devrunway-claude-plugin](https://github.com/manikumarkv/devrunway-claude-plugin) — distributed by [TomeVault](https://tomevault.io).