FastAPI - FastAPI

FastAPI framework, high performance, easy to learn, fast to code, ready for production
Documentation: https://fastapi.tiangolo.com
Source Code: https://github.com/fastapi/fastapi
FastAPI is a modern, fast (high-performance), web framework for building APIs with Python based on standard Python type hints.
Use the official FastAPI skill for your installed version. Install it from your project directory:
See Develop with AI.
The key features are:
* estimation based on tests conducted by an internal development team, building production applications.
"[...] I'm using FastAPI a ton these days. [...] I'm actually planning to use it for all of my team's ML services at Microsoft. Some of them are getting integrated into the core Windows product and some Office products."
"We adopted the FastAPI library to spawn a REST server that can be queried to obtain predictions. [for Ludwig]"
"Netflix is pleased to announce the open-source release of our crisis management orchestration framework: Dispatch! [built with FastAPI]"
"If anyone is looking to build a production Python API, I would highly recommend FastAPI. It is beautifully designed, simple to use and highly scalable, it has become a key component in our API first development strategy and is driving many automations and services such as our Virtual TAC Engineer."
There's a FastAPI mini documentary released at the end of 2025, you can watch it online:
If you are building a CLI app to be used in the terminal instead of a web API, check out Typer.
Typer is FastAPI's little sibling. And it's intended to be the FastAPI of CLIs. ⌨️ 🚀
FastAPI stands on the shoulders of giants:
First, install uv, and then add FastAPI to your project:
Note: Make sure you put "fastapi[standard]" in quotes to ensure it works in all terminals.
If you prefer to use pip, install fastapi[standard] inside a virtual environment. See the installation guide for the alternative steps.
Create a file main.py with:
If your code uses async / await, use async def:
If you don't know, check the "In a hurry?" section about async and await in the docs.
Run the server with:
The command fastapi dev reads your main.py file automatically, detects the FastAPI app in it, and starts a server using Uvicorn.
By default, fastapi dev will start with auto-reload enabled for local development.
You can read more about it in the FastAPI CLI docs.
Open your browser at http://127.0.0.1:8000/items/5?q=somequery.
You will see the JSON response as:
You already created an API that:
Now go to http://127.0.0.1:8000/docs.
You will see the automatic interactive API documentation (provided by Swagger UI):
And now, go to http://127.0.0.1:8000/redoc.
You will see the alternative automatic documentation (provided by ReDoc):
Now modify the file main.py to receive a body from a PUT request.
Declare the body using standard Python types, thanks to Pydantic.
The fastapi dev server should reload automatically.
Now go to http://127.0.0.1:8000/docs.
And now, go to http://127.0.0.1:8000/redoc.
In summary, you declare once the types of parameters, body, etc. as function parameters.
You do that with standard modern Python types.