---
title: FastAPI
description: Build Python Workers APIs using FastAPI with the built-in ASGI server.
image: https://developers.cloudflare.com/dev-products-preview.png
---

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# FastAPI

The FastAPI package is supported in Python Workers.

FastAPI applications use a protocol called the [Asynchronous Server Gateway Interface (ASGI) ↗](https://asgi.readthedocs.io/en/latest/). This means that FastAPI never reads from or writes to a socket itself. An ASGI application expects to be hooked up to an ASGI server, typically [uvicorn ↗](https://uvicorn.dev/). The ASGI server handles all of the raw sockets on the application’s behalf.

The Python Workers provides [an ASGI server ↗](https://github.com/cloudflare/workers-py/blob/main/packages/runtime-sdk/src/asgi.py)that you can use directly in your Python Worker, which lets you use FastAPI in Python Workers.

## Get Started

Clone the `cloudflare/python-workers-examples` repository and run the FastAPI example:

Terminal window

```
git clone https://github.com/cloudflare/python-workers-examplescd python-workers-examples/03-fastapiuv run pywrangler dev
```

### Example code

Python

```
from workers import WorkerEntrypointfrom fastapi import FastAPI, Requestfrom pydantic import BaseModelimport asgi
class Default(WorkerEntrypoint):    async def fetch(self, request):        return await asgi.fetch(app, request, self.env)
app = FastAPI()
@app.get("/")async def root():    return {"message": "Hello, World!"}
@app.get("/env")async def root(req: Request):    env = req.scope["env"]    return {"message": "Here is an example of getting an environment variable: " + env.MESSAGE}
class Item(BaseModel):    name: str    description: str | None = None    price: float    tax: float | None = None
@app.post("/items/")async def create_item(item: Item):    return item
@app.put("/items/{item_id}")async def create_item(item_id: int, item: Item, q: str | None = None):    result = {"item_id": item_id, **item.dict()}    if q:        result.update({"q": q})    return result
@app.get("/items/{item_id}")async def read_item(item_id: int):    return {"item_id": item_id}
```

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