Pydantic

Pydantic is a Python library for data validation and settings management using Python type annotations. It enforces type hints at runtime and provides clear, user-friendly error messages when data is invalid. Pydantic is widely used in FastAPI for request body parsing, and in CLI and configuration tools for parsing environment variables and config files via BaseSettings. At its core, you define a model by subclassing BaseModel and annotating fields with types — Pydantic handles all coercion, validation, and serialization automatically.