fastapi

Production-ready FastAPI patterns with Pydantic v2, SQLAlchemy 2.0 async, and JWT authentication. Production-tested patterns for FastAPI with Pydantic v2, SQLAlchemy 2.0 async, and JWT authentication. Latest Versions (verified January 2026): Requirements : Run: uv run fastapi dev src/main.py Docs available at: For maintainable projects, organize by domain not file type: Key Points : Create .env : This skill prevents 7 documented issues from official FastAPI GitHub and release notes. Error : model.model_fields_set includes default values when using Form() Source : GitHub Issue #13399 Why It Happens : Form data parsing preloads default values and passes them to the validator, making it impossible to distinguish between fields explicitly set by the user and fields using defaults. This bug ONLY affects Form data, not JSON body data. Prevention : Error : Background tasks added via BackgroundTasks dependency don't run Source : GitHub Issue #11215 Why It Happens : When you return a custom Response with a background parameter, it overwrites all tasks added to the injected BackgroundTasks dependency. This is not documented and causes silent failures. Prevention : Rule : Pick ONE mechanism and stick with it.