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https://github.com/tiangolo/fastapi

FastAPI framework, high performance, easy to learn, fast to code, ready for production
https://github.com/tiangolo/fastapi

api async asyncio fastapi framework json json-schema openapi openapi3 pydantic python python-types python3 redoc rest starlette swagger swagger-ui uvicorn web

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FastAPI framework, high performance, easy to learn, fast to code, ready for production

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  FastAPI





    FastAPI framework, high performance, easy to learn, fast to code, ready for production







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---



**Documentation**: https://fastapi.tiangolo.com



**Source Code**: https://github.com/tiangolo/fastapi



---



FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.8+ based on standard Python type hints.



The key features are:



* **Fast**: Very high performance, on par with **NodeJS** and **Go** (thanks to Starlette and Pydantic). [One of the fastest Python frameworks available](#performance).

* **Fast to code**: Increase the speed to develop features by about 200% to 300%. *

* **Fewer bugs**: Reduce about 40% of human (developer) induced errors. *

* **Intuitive**: Great editor support. Completion everywhere. Less time debugging.

* **Easy**: Designed to be easy to use and learn. Less time reading docs.

* **Short**: Minimize code duplication. Multiple features from each parameter declaration. Fewer bugs.

* **Robust**: Get production-ready code. With automatic interactive documentation.

* **Standards-based**: Based on (and fully compatible with) the open standards for APIs: OpenAPI (previously known as Swagger) and JSON Schema.



* estimation based on tests on an internal development team, building production applications.



## Sponsors




































Other sponsors



## Opinions



"_[...] 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._"



Kabir Khan - Microsoft (ref)




---



"_We adopted the **FastAPI** library to spawn a **REST** server that can be queried to obtain **predictions**. [for Ludwig]_"



Piero Molino, Yaroslav Dudin, and Sai Sumanth Miryala - Uber (ref)




---



"_**Netflix** is pleased to announce the open-source release of our **crisis management** orchestration framework: **Dispatch**! [built with **FastAPI**]_"



Kevin Glisson, Marc Vilanova, Forest Monsen - Netflix (ref)




---



"_I’m over the moon excited about **FastAPI**. It’s so fun!_"



Brian Okken - Python Bytes podcast host (ref)




---



"_Honestly, what you've built looks super solid and polished. In many ways, it's what I wanted **Hug** to be - it's really inspiring to see someone build that._"



Timothy Crosley - Hug creator (ref)




---



"_If you're looking to learn one **modern framework** for building REST APIs, check out **FastAPI** [...] It's fast, easy to use and easy to learn [...]_"



"_We've switched over to **FastAPI** for our **APIs** [...] I think you'll like it [...]_"



Ines Montani - Matthew Honnibal - Explosion AI founders - spaCy creators (ref) - (ref)




---



"_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._"



Deon Pillsbury - Cisco (ref)




---



## **Typer**, the FastAPI of CLIs






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**. ⌨️ 🚀



## Requirements



Python 3.8+



FastAPI stands on the shoulders of giants:



* Starlette for the web parts.

* Pydantic for the data parts.



## Installation






```console

$ pip install fastapi



---> 100%

```






You will also need an ASGI server, for production such as Uvicorn or Hypercorn.






```console

$ pip install "uvicorn[standard]"



---> 100%

```






## Example



### Create it



* Create a file `main.py` with:



```Python

from typing import Union



from fastapi import FastAPI



app = FastAPI()



@app.get("/")

def read_root():

    return {"Hello": "World"}



@app.get("/items/{item_id}")

def read_item(item_id: int, q: Union[str, None] = None):

    return {"item_id": item_id, "q": q}

```



Or use async def...



If your code uses `async` / `await`, use `async def`:



```Python hl_lines="9  14"

from typing import Union



from fastapi import FastAPI



app = FastAPI()



@app.get("/")

async def read_root():

    return {"Hello": "World"}



@app.get("/items/{item_id}")

async def read_item(item_id: int, q: Union[str, None] = None):

    return {"item_id": item_id, "q": q}

```



**Note**:



If you don't know, check the _"In a hurry?"_ section about `async` and `await` in the docs.



### Run it



Run the server with:






```console

$ uvicorn main:app --reload



INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

INFO:     Started reloader process [28720]

INFO:     Started server process [28722]

INFO:     Waiting for application startup.

INFO:     Application startup complete.

```






About the command uvicorn main:app --reload...



The command `uvicorn main:app` refers to:



* `main`: the file `main.py` (the Python "module").

* `app`: the object created inside of `main.py` with the line `app = FastAPI()`.

* `--reload`: make the server restart after code changes. Only do this for development.



### Check it



Open your browser at http://127.0.0.1:8000/items/5?q=somequery.



You will see the JSON response as:



```JSON

{"item_id": 5, "q": "somequery"}

```



You already created an API that:



* Receives HTTP requests in the _paths_ `/` and `/items/{item_id}`.

* Both _paths_ take `GET` operations (also known as HTTP _methods_).

* The _path_ `/items/{item_id}` has a _path parameter_ `item_id` that should be an `int`.

* The _path_ `/items/{item_id}` has an optional `str` _query parameter_ `q`.



### Interactive API docs



Now go to http://127.0.0.1:8000/docs.



You will see the automatic interactive API documentation (provided by Swagger UI):



![Swagger UI](https://fastapi.tiangolo.com/img/index/index-01-swagger-ui-simple.png)



### Alternative API docs



And now, go to http://127.0.0.1:8000/redoc.



You will see the alternative automatic documentation (provided by ReDoc):



![ReDoc](https://fastapi.tiangolo.com/img/index/index-02-redoc-simple.png)



## Example upgrade



Now modify the file `main.py` to receive a body from a `PUT` request.



Declare the body using standard Python types, thanks to Pydantic.



```Python hl_lines="4  9-12  25-27"

from typing import Union



from fastapi import FastAPI

from pydantic import BaseModel



app = FastAPI()



class Item(BaseModel):

    name: str

    price: float

    is_offer: Union[bool, None] = None



@app.get("/")

def read_root():

    return {"Hello": "World"}



@app.get("/items/{item_id}")

def read_item(item_id: int, q: Union[str, None] = None):

    return {"item_id": item_id, "q": q}



@app.put("/items/{item_id}")

def update_item(item_id: int, item: Item):

    return {"item_name": item.name, "item_id": item_id}

```



The server should reload automatically (because you added `--reload` to the `uvicorn` command above).



### Interactive API docs upgrade



Now go to http://127.0.0.1:8000/docs.



* The interactive API documentation will be automatically updated, including the new body:



![Swagger UI](https://fastapi.tiangolo.com/img/index/index-03-swagger-02.png)



* Click on the button "Try it out", it allows you to fill the parameters and directly interact with the API:



![Swagger UI interaction](https://fastapi.tiangolo.com/img/index/index-04-swagger-03.png)



* Then click on the "Execute" button, the user interface will communicate with your API, send the parameters, get the results and show them on the screen:



![Swagger UI interaction](https://fastapi.tiangolo.com/img/index/index-05-swagger-04.png)



### Alternative API docs upgrade



And now, go to http://127.0.0.1:8000/redoc.



* The alternative documentation will also reflect the new query parameter and body:



![ReDoc](https://fastapi.tiangolo.com/img/index/index-06-redoc-02.png)



### Recap



In summary, you declare **once** the types of parameters, body, etc. as function parameters.



You do that with standard modern Python types.



You don't have to learn a new syntax, the methods or classes of a specific library, etc.



Just standard **Python 3.8+**.



For example, for an `int`:



```Python

item_id: int

```



or for a more complex `Item` model:



```Python

item: Item

```



...and with that single declaration you get:



* Editor support, including:

    * Completion.

    * Type checks.

* Validation of data:

    * Automatic and clear errors when the data is invalid.

    * Validation even for deeply nested JSON objects.

* Conversion of input data: coming from the network to Python data and types. Reading from:

    * JSON.

    * Path parameters.

    * Query parameters.

    * Cookies.

    * Headers.

    * Forms.

    * Files.

* Conversion of output data: converting from Python data and types to network data (as JSON):

    * Convert Python types (`str`, `int`, `float`, `bool`, `list`, etc).

    * `datetime` objects.

    * `UUID` objects.

    * Database models.

    * ...and many more.

* Automatic interactive API documentation, including 2 alternative user interfaces:

    * Swagger UI.

    * ReDoc.



---



Coming back to the previous code example, **FastAPI** will:



* Validate that there is an `item_id` in the path for `GET` and `PUT` requests.

* Validate that the `item_id` is of type `int` for `GET` and `PUT` requests.

    * If it is not, the client will see a useful, clear error.

* Check if there is an optional query parameter named `q` (as in `http://127.0.0.1:8000/items/foo?q=somequery`) for `GET` requests.

    * As the `q` parameter is declared with `= None`, it is optional.

    * Without the `None` it would be required (as is the body in the case with `PUT`).

* For `PUT` requests to `/items/{item_id}`, Read the body as JSON:

    * Check that it has a required attribute `name` that should be a `str`.

    * Check that it has a required attribute `price` that has to be a `float`.

    * Check that it has an optional attribute `is_offer`, that should be a `bool`, if present.

    * All this would also work for deeply nested JSON objects.

* Convert from and to JSON automatically.

* Document everything with OpenAPI, that can be used by:

    * Interactive documentation systems.

    * Automatic client code generation systems, for many languages.

* Provide 2 interactive documentation web interfaces directly.



---



We just scratched the surface, but you already get the idea of how it all works.



Try changing the line with:



```Python

    return {"item_name": item.name, "item_id": item_id}

```



...from:



```Python

        ... "item_name": item.name ...

```



...to:



```Python

        ... "item_price": item.price ...

```



...and see how your editor will auto-complete the attributes and know their types:



![editor support](https://fastapi.tiangolo.com/img/vscode-completion.png)



For a more complete example including more features, see the Tutorial - User Guide.



**Spoiler alert**: the tutorial - user guide includes:



* Declaration of **parameters** from other different places as: **headers**, **cookies**, **form fields** and **files**.

* How to set **validation constraints** as `maximum_length` or `regex`.

* A very powerful and easy to use **Dependency Injection** system.

* Security and authentication, including support for **OAuth2** with **JWT tokens** and **HTTP Basic** auth.

* More advanced (but equally easy) techniques for declaring **deeply nested JSON models** (thanks to Pydantic).

* **GraphQL** integration with Strawberry and other libraries.

* Many extra features (thanks to Starlette) as:

    * **WebSockets**

    * extremely easy tests based on HTTPX and `pytest`

    * **CORS**

    * **Cookie Sessions**

    * ...and more.



## Performance



Independent TechEmpower benchmarks show **FastAPI** applications running under Uvicorn as one of the fastest Python frameworks available, only below Starlette and Uvicorn themselves (used internally by FastAPI). (*)



To understand more about it, see the section Benchmarks.



## Optional Dependencies



Used by Pydantic:



* email_validator - for email validation.

* pydantic-settings - for settings management.

* pydantic-extra-types - for extra types to be used with Pydantic.



Used by Starlette:



* httpx - Required if you want to use the `TestClient`.

* jinja2 - Required if you want to use the default template configuration.

* python-multipart - Required if you want to support form "parsing", with `request.form()`.

* itsdangerous - Required for `SessionMiddleware` support.

* pyyaml - Required for Starlette's `SchemaGenerator` support (you probably don't need it with FastAPI).

* ujson - Required if you want to use `UJSONResponse`.



Used by FastAPI / Starlette:



* uvicorn - for the server that loads and serves your application.

* orjson - Required if you want to use `ORJSONResponse`.



You can install all of these with `pip install "fastapi[all]"`.



## License



This project is licensed under the terms of the MIT license.