Introduction

Python (covered earlier) is beloved for readability, but its classic web framework Flask (the batch 18 post) was built for websites, not APIs, and leaves validation and documentation to you. FastAPI, released in 2018, is built for APIs from the ground up: declare your endpoints with Python type hints, and it validates requests, serialises responses, and generates interactive API documentation automatically. It is one of the fastest-growing Python frameworks for a reason — it removes the tedious parts of API work.

Type hints, validation, and automatic docs

FastAPI's core trick is turning Python's type hints into behaviour:

Typed endpoints — declare a function parameter as item_id: int and FastAPI rejects non-integer values with a clear error, before your code runs.

Pydantic models — define request/response shapes as classes, and FastAPI validates incoming JSON against them, converts types, and documents the schema.

Automatic docs — every endpoint appears in interactive Swagger UI and ReDoc…