FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.8+ based on standard Python type hints. It is designed to be easy to use, fast to develop with, and to provide efficient performance. FastAPI is built on top of Starlette and Pydantic.

Key features of FastAPI include :

* Fast : As the name suggests, FastAPI is designed to be fast. It leverages Python type hints and asynchronous programming to achieve high performance.

* Automatic Documentation : FastAPI generates OpenAPI and JSON Schema documentation automatically based on the Python type hints used in the code. This documentation is interactive and can be explored through Swagger UI and ReDoc.

* Type Checking : FastAPI uses Python type hints for request and response validation. This not only helps with automatic documentation but also enables the use of tools like Pydantic for data validation and serialization.

* Asynchronous Support : FastAPI fully supports asynchronous programming, allowing you to write asynchronous routes and take advantage of the performance benefits of asynchronous I/O operations.

* Dependency Injection System : FastAPI has a powerful dependency injection system that makes it easy to manage dependencies in a clean and organized way.
* Security Features : It includes features for handling security, including support for OAuth2, API key authentication, and more.

* WebSocket Support : FastAPI supports WebSocket communication, allowing real-time bidirectional communication between clients and the server.

* Compatibility with Standard Python Type Hints : FastAPI leverages Python type hints for request and response validation. This provides a clear contract for the API and allows for better tooling support.

* Compatibility with Other Web Frameworks : FastAPI is designed to be easy to integrate with other web frameworks, allowing you to use it alongside existing applications or services.

* Built-in Support for OAuth2 and JWT : FastAPI provides built-in support for OAuth2 and JSON Web Tokens (JWT) for handling authentication and authorization.