Understand the real differences between SSE and WebSockets and learn when to pick each for real-time web features.

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Introduction

So you want real-time updates in your web app.
Maybe it’s a live chat, a stock ticker, a multiplayer dashboard, or a push notification system.

You’ve probably come across two main technologies for this: Server-Sent Events (SSE) and WebSockets.

Both can stream live data from a server to a browser, but they work very differently, and each shines in specific scenarios.

In this post, you’ll learn:

• How SSE and WebSockets actually work under the hood
• Key differences in their architecture
• Performance, scalability, and browser support comparisons
• Real-world examples of when to use each

By the end, you’ll know exactly which one fits your next real-time project.

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1. The Problem: Real-Time Communication in Web Apps

Normally, web browsers use HTTP requests a one-way communication:

The client sends a request → The server responds → The connection closes.

But real-time applications need something more dynamic; they need the server to push updates automatically without waiting for the client to ask again.

For example:

• Live chat apps
• Stock price tickers
• Notifications
• Live dashboards

There are a few ways to achieve this: Polling, Server-Sent Events, and WebSockets.
Let’s skip polling (inefficient) and compare the two modern options head-to-head.

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2. What Are Server-Sent Events (SSE)?

Server-Sent Events use a unidirectional connection:
The browser opens an HTTP connection to the server, and the server keeps it open to push messages down whenever new data is available.

• Client → Server: one HTTP request (GET /events)
• Server → Client: continuous stream of data (text/event-stream)

The protocol is built on top of HTTP and works with EventSource, a browser API designed for this.

Basic Example

// Client-side
const eventSource = new EventSource('/stream');

eventSource.onmessage = (event) => {
  console.log('New message:', event.data);
};

// Server-side (Node.js example)
app.get('/stream', (req, res) => {
  res.setHeader('Content-Type', 'text/event-stream');
  res.setHeader('Cache-Control', 'no-cache');
  res.setHeader('Connection', 'keep-alive');

  setInterval(() => {
    res.write(`data: ${new Date().toISOString()}\n\n`);
  }, 1000);
});

✅ The browser keeps the connection open, and the server pushes updates automatically.

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How It Works Internally

• The client makes an HTTP GET request.
• The server responds with a special text/event-stream content type.
• The connection remains open (no closing after response).
• Messages are sent as lines of text, ending with a double newline.
• The browser EventSource automatically reconnects if the connection drops.

It’s simple, stable, and works great for server-to-client data streaming.

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3. What Are WebSockets?

WebSockets provide full-duplex (two-way) communication over a single TCP connection.

That means both client and server can send and receive data at any time simultaneously.

It starts with an HTTP handshake, then “upgrades” the connection to the WebSocket protocol, which operates outside the normal HTTP request-response cycle.

Basic Example

// Client-side
const socket = new WebSocket('ws://localhost:3000');

socket.onopen = () => console.log('Connected');
socket.onmessage = (event) => console.log('Server says:', event.data);
socket.send('Hello Server!');

// Server-side (Node.js)
const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 3000 });

wss.on('connection', (socket) => {
  console.log('Client connected');
  socket.on('message', (msg) => console.log('Received:', msg));
  setInterval(() => socket.send(new Date().toISOString()), 1000);
});

✅ Both sides can send messages at any time, ideal for chat apps, games, and collaborative tools.

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4. Key Differences Between SSE and WebSockets

In short:

• SSE is simpler and more reliable for server → client updates.
• WebSockets are more powerful for two-way communication.

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5. When to Use Server-Sent Events (SSE)

SSEs are perfect when your app only needs to push updates from the server to the browser.

Best Use Cases

• News feeds or live dashboards
• Stock price tickers
• Real-time logs or system monitoring
• Notifications or progress updates
• Chat message delivery (server → client only)

Why It’s Great

• Works over HTTP/HTTPS (no special ports).
• Automatically reconnects on failure.
• Lightweight and text-based.
• Integrates well with CDN and reverse proxies.
• Very simple to implement.

Example Use Case: Live Notifications

const eventSource = new EventSource('/notifications');
eventSource.onmessage = (e) => showToast(e.data);

You can scale this easily behind load balancers, no special setup required.

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6. When to Use WebSockets

WebSockets are ideal when you need true two-way, low-latency communication, especially when both client and server need to send messages freely.

Best Use Cases

• Chat and messaging systems
• Multiplayer games
• Real-time collaboration (Google Docs-style editing)
• IoT data streaming
• Trading platforms or live dashboards requiring bi-directional sync

Why It’s Great

• Minimal latency (no polling or re-requesting).
• Full-duple,x both sides can send at any time.
• Can handle binary and text data.
• Integrates with backend frameworks like Socket.IO for extra reliability.

Example Use Case: Live Chat

const socket = new WebSocket('wss://example.com/chat');

socket.onmessage = (e) => renderMessage(e.data);
document.querySelector('form').onsubmit = (e) => {
  e.preventDefault();
  socket.send(input.value);
  input.value = '';
};

This is where WebSockets truly shine: low-latency, continuous two-way interaction.

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7. Performance & Scalability

If you’re using modern infrastructure (like NGINX, AWS ALB, or Cloudflare), both are supported, but SSE scales better with existing HTTP infrastructure.

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8. Browser and Server Support

All modern browsers support both, but SSE is slightly simpler to set up if you don’t need two-way data.

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9. Choosing the Right One: Quick Decision Guide

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10. Real-World Hybrid Example

Some modern systems even use both:

• SSE for real-time server updates (notifications, logs)
• WebSockets for interactive features (chat, user actions)

For example, GitHub uses SSE for real-time notifications, while collaborative tools like Figma and Trello rely on WebSockets for live interaction.

You can also fall back from WebSockets to SSE if sockets fail; frameworks like Socket.IO and Phoenix Channels handle that automatically.

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Conclusion

Both Server-Sent Events and WebSockets give you real-time capabilities, but they serve different needs.

• Choose SSE for simple, one-way updates (dashboards, feeds, notifications).
• Choose WebSockets for full two-way communication (chats, multiplayer, live editors).

If your app doesn’t require constant back-and-forth data, SSE is lighter, simpler, and scales better.
But if you need continuous, interactive messaging, WebSockets are the gold standard.

Pro Tip: Start with SSE; you can always upgrade to WebSockets when your app grows more interactive.

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Call to Action

Have you used SSE or WebSockets in your projects?
Which one felt easier to scale or integrate?
Share your experience in the comments and bookmark this post for when you build your next real-time web feature.