FastAPI: Automatic Interactive API Docs

FastAPI turns your Python type hints and Pydantic models into live, interactive API documentation, making your code the single source of truth. It automatically generates an OpenAPI schema and serves it via Swagger UI (`/docs`) for interactive testing and ReDoc (`/redoc`) for clean documentation. The main footgun is assuming the types are enough; always add explicit descriptions via docstrings to clarify the *why* behind an endpoint, not just the *what*.