fastapi/docs/en/docs/advanced/websockets.md

WebSockets

You can use WebSockets with FastAPI.

WebSockets client

In production

In your production system, you probably have a frontend created with a modern framework like React, Vue.js or Angular.

And to communicate using WebSockets with your backend you would probably use your frontend's utilities.

Or you might have a native mobile application that communicates with your WebSocket backend directly, in native code.

Or you might have any other way to communicate with the WebSocket endpoint.

---

But for this example, we'll use a very simple HTML document with some JavaScript, all inside a long string.

This, of course, is not optimal and you wouldn't use it for production.

In production you would have one of the options above.

But it's the simplest way to focus on the server-side of WebSockets and have a working example:

{!../../../docs_src/websockets/tutorial001.py!}

Create a websocket

In your FastAPI application, create a websocket:

{!../../../docs_src/websockets/tutorial001.py!}

!!! note "Technical Details" You could also use from starlette.websockets import WebSocket.

**FastAPI** provides the same `WebSocket` directly just as a convenience for you, the developer. But it comes directly from Starlette.

Await for messages and send messages

In your WebSocket route you can await for messages and send messages.

{!../../../docs_src/websockets/tutorial001.py!}

You can receive and send binary, text, and JSON data.

Try it

If your file is named main.py, run your application with:

$ uvicorn main:app --reload

<span style="color: green;">INFO</span>:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

Open your browser at http://127.0.0.1:8000.

You will see a simple page like:

You can type messages in the input box, and send them:

And your FastAPI application with WebSockets will respond back:

You can send (and receive) many messages:

And all of them will use the same WebSocket connection.

Using Depends and others

In WebSocket endpoints you can import from fastapi and use:

• Depends
• Security
• Cookie
• Header
• Path
• Query

They work the same way as for other FastAPI endpoints/path operations:

{!../../../docs_src/websockets/tutorial002.py!}

!!! info In a WebSocket it doesn't really make sense to raise an HTTPException. So it's better to close the WebSocket connection directly.

You can use a closing code from the <a href="https://tools.ietf.org/html/rfc6455#section-7.4.1" class="external-link" target="_blank">valid codes defined in the specification</a>.

In the future, there will be a `WebSocketException` that you will be able to `raise` from anywhere, and add exception handlers for it. It depends on the <a href="https://github.com/encode/starlette/pull/527" class="external-link" target="_blank">PR #527</a> in Starlette.

Try the WebSockets with dependencies

If your file is named main.py, run your application with:

$ uvicorn main:app --reload

<span style="color: green;">INFO</span>:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

Open your browser at http://127.0.0.1:8000.

There you can set:

• The "Item ID", used in the path.
• The "Token" used as a query parameter.

!!! tip Notice that the query token will be handled by a dependency.

With that you can connect the WebSocket and then send and receive messages:

More info

To learn more about the options, check Starlette's documentation for:

• The WebSocket class.
• Class-based WebSocket handling.