FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.6+ based on standard Python type hints. One of the key features that sets FastAPI apart from other frameworks is its speed. In this post, we will explore the reasons why FastAPI is fast and how it achieves its high performance.

Async Support

FastAPI is built on top of Starlette for handling HTTP requests, and uses the new asynchronous features introduced in Python 3.6 to handle multiple requests at the same time without blocking. Asynchronous programming allows for a non-blocking, event-driven approach to handle multiple requests simultaneously, which results in a significant performance boost.

FastAPI uses Pydantic

FastAPI uses Pydantic for data validation and settings management. Pydantic models are used for request bodies, query parameters and headers validation. Pydantic uses type hints for data validation, which makes the process of validation very fast as well as easy to understand.

Automatic API documentation

FastAPI provides automatic API documentation using the popular library Swagger UI and ReDoc. These libraries allow you to easily generate interactive API documentation, which can be helpful for both developers and end-users. However, this feature is optional and can be turned off if it's not needed, which can lead to even faster performance.

High-performance web server

FastAPI is built on top of Starlette, which is a lightweight web framework that can run on the asynchronous web server ASGI. ASGI is a specification for asynchronous servers, which is faster than WSGI, the specification for synchronous servers that most other Python web frameworks use.


FastAPI is fast because it makes use of the latest features of Python and the best libraries to provide a high-performance web framework. The use of asynchronous programming, Pydantic for data validation, automatic API documentation, and a high-performance web server all contribute to the speed and performance of FastAPI. If you're looking for a fast and easy-to-use web framework for your next project, FastAPI is definitely worth considering.

Why is FastAPI Fast?