FastAPI is a modern, high-performance Python web framework specifically designed for building APIs quickly and efficiently. It’s built on top of Starlette for web handling and Pydantic for data validation, offering automatic documentation, type hints, and validation without extra configuration. Developers choose FastAPI because it enables rapid development while maintaining clean, readable code, and is highly suitable for both small projects and large-scale, production-ready applications requiring speed, reliability, and maintainability.