fastapi

Use when working with FastAPI endpoints, Pydantic v2 models, dependency injection, middleware, background tasks, WebSockets, or streaming responses. Also use when testing FastAPI with httpx/TestClient, deploying with uvicorn, or debugging async route handling and OpenAPI schema generation.

Model	Source
sonnet	pack: python

Full Reference

fastapi

FastAPI is an async-first Python web framework built on Starlette and Pydantic v2. It auto-generates OpenAPI (Swagger) docs from type annotations. Pydantic v1 support is deprecated — use Pydantic v2 patterns throughout.

Quick Reference

Item	Value
Install	pip install fastapi uvicorn[standard]
Pydantic version	v2 — model_config = ConfigDict(from_attributes=True) (not orm_mode)
Dev server	uvicorn main:app --reload
Prod server	gunicorn main:app -w 4 -k uvicorn.workers.UvicornWorker
Docs URL	/docs (Swagger) and /redoc
Background tasks limit	30s max — use Celery/ARQ for longer work

Reference Index

I want to…	File
Set up the app, CORS middleware, and lifespan hooks	reference/app-setup.md
Define path operations (GET, POST, PUT, DELETE) with query/path params	reference/path-operations.md
Write Pydantic v2 request/response models and validators	reference/pydantic-models.md
Implement dependency injection for DB sessions and auth	reference/dependency-injection.md
Add streaming responses, WebSockets, background tasks, and file uploads	reference/advanced-features.md
Test FastAPI routes with httpx and pytest-asyncio	reference/testing.md

Usage: Read the reference file matching your current task from the index above. Each file is self-contained with code examples and inline gotchas.

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Announcement

┏━ ⚡ fastapi ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓ ┃ Async Python API framework with Pydantic v2 and auto OpenAPI docs ┃ ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛