Modern web applications are becoming increasingly real-time. Users expect live notifications, dashboards that update automatically, chat-like experiences, and instant status updates without constantly refreshing the page.
While WebSockets often steal the spotlight, Server-Sent Events (SSE) are frequently the better choice for many applications.
So when should you use Server-Sent Events, and when should you avoid them?
Let's dive in.
What Are Server-Sent Events?
Server-Sent Events (SSE) allow a server to push data to a client over a single long-lived HTTP connection.
Unlike traditional HTTP requests where the client asks for updates repeatedly (polling), SSE keeps the connection open, allowing the server to send new information whenever it becomes available.
The browser provides native support through the EventSource API.
const source = new EventSource("/events");
source.onmessage = (event) => {
console.log(event.data);
};
That's all it takes to start receiving real-time updates.
How SSE Works
The communication flow looks like this:
Client
|
| GET /events
|
Server
|
| Connection stays open
|
| ---> Update #1
| ---> Update #2
| ---> Update #3
| ---> ...
The server continuously streams events without requiring additional requests.
Advantages of Server-Sent Events
- Extremely Simple
Compared to WebSockets, SSE requires very little setup.
No handshake protocols.
No socket libraries.
No message serialization logic.
If your backend already serves HTTP requests, adding SSE is usually straightforward.
- Built on Standard HTTP
Because SSE uses normal HTTP:
Reverse proxies work naturally
Authentication works the same
Cookies are automatically included
HTTPS behaves exactly as expected
This makes deployment much easier than custom socket servers.
- Automatic Reconnection
One of the nicest features of SSE is that browsers reconnect automatically if the connection drops.
If the user temporarily loses internet connectivity, the browser retries without any extra code.
const events = new EventSource("/events");
That's it.
No reconnect loops.
No exponential backoff implementation.
- Lightweight
Unlike WebSockets, SSE sends plain text over HTTP.
There is very little protocol overhead.
For applications broadcasting frequent updates to many clients, this can be surprisingly efficient.
Great Use Cases for SSE
SSE shines whenever information flows from the server to the client.
Live Notifications
Examples:
New messages
Friend requests
Payment confirmations
Order status
Whenever something happens on the server, push it immediately.
Dashboards
Imagine monitoring:
Website traffic
Active users
CPU usage
Memory consumption
Sales statistics
Instead of refreshing every few seconds, updates appear automatically.
Perfect for admin dashboards.
Stock Prices
Financial applications often need one-way updates.
Apple: 219.31
Apple: 219.48
Apple: 219.12
SSE streams price changes efficiently.
Sports Scores
Live scoreboards are an ideal example.
Goal!
Manchester 2
Liverpool 1
No polling required.
News Feeds
Breaking news applications frequently push updates as articles are published.
Users instantly receive new content.
Build Progress
Developers often use SSE for long-running tasks.
Imagine uploading a video:
Encoding...
12%
Encoding...
38%
Encoding...
72%
Finished!
The server continuously reports progress.
AI Streaming Responses
Many modern AI applications stream generated text token by token.
Instead of waiting 20 seconds for an entire response, users see:
Hello...
Hello there...
Hello there! Today we'll...
This dramatically improves perceived performance.
Many AI providers use SSE for exactly this reason.
When SSE Is Better Than Polling
Polling typically looks like this:
Every 5 seconds
Client
|
GET /updates
|
Response
Most of the time the server replies:
No updates.
That's wasted bandwidth.
SSE eliminates unnecessary requests because updates are only sent when something actually changes.
When SSE Is Better Than WebSockets
Many developers immediately reach for WebSockets when they hear "real-time."
But WebSockets aren't always the best tool.
Choose SSE if:
Data flows mostly one direction
Clients only receive updates
Simplicity is important
HTTP infrastructure already exists
You don't need binary messages
SSE is often significantly easier to implement and maintain.
When NOT to Use SSE
SSE isn't suitable for every application.
Avoid it if your application requires constant communication in both directions.
Chat Applications
Users both:
send messages
receive messages
While you can combine SSE with regular HTTP POST requests, WebSockets usually provide a cleaner solution.
Multiplayer Games
Games require:
very low latency
bidirectional communication
frequent updates
WebSockets are the better choice.
Collaborative Editors
Applications like collaborative document editors require continuous updates from every participant.
WebSockets handle this much more naturally.
Voice or Video Streaming
SSE only supports text.
It cannot stream binary data efficiently.
SSE Limitations
Although useful, SSE has some drawbacks.
One-Way Communication
Clients cannot send data through the same connection.
They must use standard HTTP requests.
Text Only
SSE transmits UTF-8 text.
Binary data must be encoded, which increases payload size.
Browser Connection Limits
Browsers may limit the number of simultaneous SSE connections per origin, particularly when using HTTP/1.1. While HTTP/2 helps alleviate many of these limitations by multiplexing multiple streams over a single connection, it's still worth considering if your application opens many concurrent event streams.
Not Ideal for Massive Two-Way Traffic
If clients constantly send and receive messages, WebSockets are a better architectural fit.
Simple Decision Guide
RequirementBest Choice
Live notifications✅ SSE
Dashboard updates✅ SSE
AI response streaming✅ SSE
Progress updates✅ SSE
Live sports scores✅ SSE
Stock prices✅ SSE
Chat application✅ WebSockets
Multiplayer game✅ WebSockets
Collaborative editor✅ WebSockets
Voice or video streaming✅ WebSockets
Final Thoughts
Server-Sent Events are often overlooked, but they provide one of the simplest and most effective ways to build real-time web applications.
If your application primarily needs to push updates from the server to the client, SSE offers a lightweight, reliable solution with minimal complexity. Features like automatic reconnection, native browser support, and seamless integration with existing HTTP infrastructure make it an excellent choice for notifications, dashboards, live feeds, AI streaming, and progress updates.
Before reaching for WebSockets, ask yourself a simple question:
Does the client really need to send real-time messages back to the server?
If the answer is no, then Server-Sent Events may be the simplest—and often the best—solution for your application.
