Real time communication is a defining feature of many modern applications. Whether you are building a live chat, a game, or a collaborative tool, you need a way for data to move instantly between clients and the server. This is where WebSockets come in.
Unlike traditional HTTP, which opens a new connection for every request and response, WebSockets maintain an open connection that allows both the server and client to send messages at any time. This persistent link makes WebSockets the perfect choice for real time messaging systems.
Python, combined with FastAPI, makes it easy to create a WebSocket server that is efficient, clear, and scalable. In this article, we will walk through the basic components required to create a working WebSocket connection between your server and the browser.
Let’s begin with the backend. FastAPI is a modern web framework that supports asynchronous programming out of the box. It allows you to define a WebSocket endpoint with just a few lines of code. Once a connection is accepted, your server can receive messages, send replies, and manage user sessions all within a single function.
This simplicity does not come at the expense of power. You can easily track multiple users, broadcast messages, and integrate with databases or task queues. FastAPI is built on Starlette, which is a powerful ASGI framework that handles real time protocols natively.
On the frontend, the browser provides a built-in WebSocket API that lets JavaScript connect to your server and send or receive messages. You do not need any extra libraries. A few lines of JavaScript can establish a connection, handle incoming messages, and update the user interface in real time.
Once the connection is open, data can flow freely. When a user sends a message, your script transmits it to the server. The server then forwards it to other connected clients. With this two way communication, your app feels immediate and dynamic, just like users expect.
A minimal implementation includes these key pieces:
- A FastAPI server with a WebSocket route
- A simple HTML page with a JavaScript WebSocket client
- A way to send and display messages between client and server
You can test this setup locally using uvicorn, which serves as the asynchronous server for your FastAPI app. Once the app is running, your frontend can connect using the WebSocket protocol. For local testing, this would look like ws://localhost:8000/ws.
The most important thing to remember is that WebSocket communication is event driven. You do not wait for a response after sending a message. Instead, your code listens for messages from the other side and handles them as they arrive. This makes it essential to design your interface to react to changes in state and content quickly.
Here are a few ideas for expanding the initial setup:
- Add user identifiers so messages show who sent what
- Create multiple chat rooms by using different endpoints or parameters
- Log all messages to a file or database for history and analysis
- Display typing indicators or connection status in the interface
- Handle disconnections and reconnections gracefully
Even a basic WebSocket application teaches valuable concepts like asynchronous programming, connection management, and event handling. These skills transfer well to any real time system.
If you want to go further and build a complete chat application with authentication, chat rooms, media sharing, and production ready deployment, I have written a 17 page PDF guide that covers the entire process. It is titled Mastering Real-Time Chat Applications Like a Pro and is available for just five dollars.
The guide takes you from designing the backend with FastAPI and WebSockets to crafting a responsive frontend with HTML and JavaScript. You will also learn how to implement modern features like message persistence, typing indicators, file sharing, and user authentication. Finally, it walks you through professional deployment using Docker, Uvicorn, Nginx, and HTTPS with Let’s Encrypt. It is ideal for developers who want to create polished and scalable chat apps using Python.
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