What it does
FastAPI is a Python framework for implementing HTTP API endpoints. Function signatures and type hints describe path parameters and request data, while the framework produces an OpenAPI schema and interactive documentation for the routes. It is a code library for building an API server, not a hosted API service or a client that calls someone else's API.
A first FastAPI example can fit in one Python file: create a FastAPI instance, decorate a function for a route, and return a small JSON object. The official guide then starts the development server and opens generated interactive documentation, so the developer can compare the declared route with the schema and try the endpoint from a browser. The framework uses Python type hints to describe inputs and generate an OpenAPI schema. That makes it practical for a small service whose request and response shapes should be visible to both client developers and API tooling. As the service grows, the tutorial extends the same path-operation approach to parameters and request bodies, rather than asking the developer to maintain a separate API document by hand. FastAPI remains the server-side framework: the project owner supplies the Python environment and chooses where to run and deploy the application. The official site also links to FastAPI Cloud, which is a separate hosted product and is not covered here. The project repository carries the MIT License. Django is a related Python project, but its tutorial centers on full web applications and admin workflows rather than this focused API-server role.
Strengths
- Route functions and Python type hints define API inputs in the application code.
- The framework generates an OpenAPI schema and interactive documentation for declared routes.
- The official tutorial expands from a minimal endpoint to path parameters and request bodies.
Watch out for
- FastAPI provides the framework, not managed hosting; the application owner must choose and operate a deployment environment.
Best for
- Python developers implementing JSON or HTTP APIs.
- Teams that want API schemas and interactive documentation derived from route definitions.
- Services whose request parameters and bodies can be described with Python types.
Sources
- FastAPI (Oct 25, 2026)
- First Steps (Oct 25, 2026)
- Tutorial - User Guide (Oct 25, 2026)
- fastapi/fastapi (Oct 25, 2026)
- MIT License (Oct 25, 2026)