Building Real-Time Apps with Server-Sent Events vs. WebSockets

In a world where digital interactions are expected to be fast, smooth, and immediate, real-time communication is no longer just a nice-to-have—it’s a necessity. Whether you’re building a stock trading dashboard, a collaborative document editor, or a customer support chat tool, how you architect your real-time communication layer can have a massive impact on performance, scalability, and developer experience.

Among the top technologies developers consider when adding real-time features to web apps are Server-Sent Events (SSE) and WebSockets. While both serve the purpose of enabling real-time data updates, they come with their own strengths, limitations, and use-case sweet spots.

If you’re building real-time apps with Server-Sent Events vs. WebSockets in mind, this guide is your deep dive into when, why, and how to choose the right one—and what to expect along the way.

Understanding Real-Time Communication in the Browser

Before we get into the comparison of Server-Sent Events vs. WebSockets, let’s quickly recap what real-time communication really means in web development.

At a high level, real-time apps allow the server to push updates to the client as soon as they happen—without requiring the client to constantly poll for updates. This approach is essential for:

Live chat systems
Sports or news score tickers
Multiplayer games
IoT dashboards
Collaborative tools like whiteboards and docs

Traditionally, this was achieved using long-polling, which involved frequent HTTP requests that kept the connection open until the server had something to respond with. But that approach is inefficient and outdated. Enter: Server-Sent Events and WebSockets.

What Are Server-Sent Events (SSE)?

Server-Sent Events are a browser-native way to establish a unidirectional stream from the server to the browser over HTTP. You can think of SSE as a server’s way of “subscribing” the client to updates.

The key characteristics of SSE:

One-way communication: From server to client only
Built on HTTP: Uses standard HTTP protocol
Text-based format: Sends messages in UTF-8 text
Automatic reconnection: The browser handles disconnections and reconnects on its own
Simple implementation: You can create an event stream with just a few lines of code

A basic example in the frontend might look like this:

const eventSource = new EventSource('/events');
eventSource.onmessage = (event) => {
  console.log("New message:", event.data);
};

And on the server (in Node.js, for instance):

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

  res.write(`data: Hello client\n\n`);

  const interval = setInterval(() => {
    res.write(`data: ${new Date().toISOString()}\n\n`);
  }, 5000);

  req.on('close', () => {
    clearInterval(interval);
  });
});

This setup gives you a straightforward channel to push real-time data to clients. No custom protocol, no new dependencies, no sockets.

What Are WebSockets?

WebSockets, on the other hand, are a protocol designed for full-duplex communication—allowing both the client and server to send messages independently over a single, persistent connection.

Key features of WebSockets:

Two-way communication: Client and server can talk to each other in real time
Runs over TCP: Once established, the connection is maintained as long as needed
Low latency: Great for chat apps, gaming, and high-frequency updates
Binary or text: Supports both formats

Example WebSocket client code:

const socket = new WebSocket('ws://localhost:8080');
socket.onmessage = (event) => {
  console.log("Message from server", event.data);
};
socket.send("Hello from client!");

And a basic server using Node.js with the ws library:

const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });

wss.on('connection', function connection(ws) {
  ws.send('Welcome!');
  ws.on('message', function incoming(message) {
    console.log('Received:', message);
    ws.send(`Echo: ${message}`);
  });
});

With WebSockets, you’re not just listening for updates—you’re part of the conversation.

Server-Sent Events vs. WebSockets: Side-by-Side Comparison

Let’s break it down.

Feature	Server-Sent Events (SSE)	WebSockets
Communication Direction	One-way (server → client)	Two-way (client ↔ server)
Protocol	HTTP	Custom protocol over TCP
Browser Support	Broad (except old IE/Edge)	Very broad
Reconnection Handling	Built-in (auto-reconnect)	Manual (needs custom logic)
Message Format	UTF-8 text only	Binary + text supported
Load Balancing & Proxies	Easier (HTTP-based)	More complex (WebSocket-aware infra needed)
Best Use Cases	Notifications, live feeds	Chats, games, collaborative tools
Complexity	Simple setup	More complex, needs handling

Use Cases for Server-Sent Events

Despite being unidirectional, SSE is ideal for many common real-time applications:

Live news feeds: Updates that don’t require user interaction
Notification systems: For example, alerts in admin dashboards
IoT dashboards: One-way data from device to interface
System monitoring tools: Think logs or metrics streaming

If you’re building real-time apps with Server-Sent Events vs. WebSockets and your app only needs the server to push data to the client (and not the other way around), then SSE is lightweight, scalable, and efficient.

Use Cases for WebSockets

WebSockets are best when your application needs two-way communication or very low latency. Ideal for:

Online chat: Users send and receive messages
Real-time gaming: Low-latency interaction is critical
Collaborative apps: Editing Google Docs style in real time
Stock trading platforms: Bidirectional updates
Live customer support: Back-and-forth interaction

The key is interactivity—if your user needs to send information as quickly as they receive it, WebSockets will outperform SSE every time.

Performance Considerations

When performance matters, there’s more than just latency to consider. Memory usage, connection handling, reconnections, fallback mechanisms, and message size all play a role.

SSE is more memory-efficient for streaming large volumes of server-side messages to a wide number of clients, because it leverages HTTP keep-alive.
WebSockets reduce overhead per message, especially important when you need high-frequency updates.
In unreliable networks, SSE tends to handle reconnections better and more gracefully than WebSockets.

Deployment and Infrastructure Impacts

Building real-time apps with Server-Sent Events vs. WebSockets doesn’t just affect your codebase—it changes your deployment architecture too.

With SSE:

You can use standard load balancers
Works seamlessly with most CDNs and reverse proxies
Scaling is simpler when traffic is one-directional

With WebSockets:

You need load balancers and proxies that support WebSocket upgrades (like NGINX with special config)
Sticky sessions may be required
Auto-scaling and cloud setups can be trickier

So if you’re working within constrained infrastructure or relying on shared hosting, SSE might be the more viable solution.

Developer Experience

SSE offers a simpler developer experience—especially for teams just getting started with real-time updates. You don’t need to worry about message framing, ping-pong keepalive mechanisms, or protocol upgrades.

WebSockets, while more powerful, require:

More error handling
Keepalive messages to maintain the connection
Custom logic for reconnections and retries
Extra logic to prevent memory leaks

This doesn’t make WebSockets worse—just more demanding.

Which One Should You Choose?

The big question: When building real-time apps with Server-Sent Events vs. WebSockets, which one should you go with?

Ask yourself:

Does the client need to send messages to the server? → Use WebSockets
Is the server just pushing updates like a feed or log? → SSE might be enough
Are you constrained by infrastructure (e.g., using a CDN or shared hosting)? → SSE
Is your app a chat, game, or collaborative platform? → WebSockets

Or you can go hybrid. Many apps use SSE for updates and HTTP for client actions. This pattern keeps things lightweight while still delivering real-time performance.

The Future of Real-Time: HTTP/3, WebTransport, and Beyond

While Server-Sent Events and WebSockets dominate today, new technologies like WebTransport and HTTP/3 are starting to offer alternatives that blend the benefits of both.

These newer protocols aim to solve problems like head-of-line blocking, unreliable connections, and stream multiplexing. But they’re still emerging and not as widely supported yet. So for now, SSE and WebSockets remain your go-to choices.