If you are building a UI that needs to show progress, logs, or live updates, you do not need to jump straight to WebSockets. In many cases, SSE is the simpler and more appropriate choice. It is a browser-friendly way for the server to push events to the client over HTTP. Think of it as a one-way live stream: the server sends updates, and the browser listens.
SSE is a great option when you need server → client streaming and want to keep the implementation simple.
What is SSE?
SSE stands for Server-Sent Events.
It is a browser-native way for the server to push updates to the client over HTTP.
When to use SSE
| Use SSE when | Avoid SSE when |
|---|---|
| The communication is one-way | You need bidirectional chat |
| You want to avoid polling | You need low-latency command/control flows |
| You want a lightweight HTTP-based stream | You need binary transport |
| You want the browser to handle the connection natively |
Examples:
- progress updates
- live logs
- status feeds
- task completion notifications
- AI-generated content token by token
Why use SSE instead of polling?
Polling is one of the most common used techniques for implementing such scenarios. Polling means the browser repeatedly asks the server for new data. That creates extra traffic and awkward timing.
SSE is better because:
- the browser opens a single connection
- the server sends events as they happen
- the client gets updates immediately
- you avoid repeated polling requests
For a small streaming UI, SSE is often the simplest option.
Technical Flow and Architecture
The implementation of an SSE stream relies on a simple front-to-back flow:
Backend Endpoint: The backend (e.g., ASP.NET) exposes an HTTP endpoint and writes data chunks as SSE events.
Frontend Consumer: The client-side framework (e.g., Angular) initializes a native browser
EventSourceobject to listen to the endpoint.UI Rendering: The interface listens for incoming chunks and renders the updates in real time as they arrive.
Stream End: Once complete, the application treats the closed stream as a normal finish state.
This is especially useful for progress UIs, logs, and status updates.
Reference
Full code is available here:
What this sample does
Backend
An ASP.NET endpoint sends streaming chunks as SSE.
Frontend
An Angular service creates an EventSource and exposes the stream to a component.
