WebSocket vs SSE: Which Should You Use in 2026?

Real-Time on the Web

Live cricket scores, chat messages, notifications, and AI answers that appear word by word all need the server to push data to the browser without being asked each time.

Two standard ways to do that are WebSockets and Server-Sent Events (SSE). They're often treated as interchangeable. They're not, and picking the simpler one can save you a lot of infrastructure work.

🎯 Quick Answer (30-Second Read)

• SSE: a long-lived HTTP response where the server streams events to the browser. One-way, text only, auto-reconnects, works with normal HTTP infrastructure.
• WebSocket: a persistent two-way connection. Client and server send messages any time, text or binary.
• Use SSE for live feeds, notifications, dashboards and streaming AI responses (the Claude and OpenAI APIs stream with SSE).
• Use WebSockets for chat, multiplayer games and collaborative editing, where both sides talk constantly.
• Not sure? If the client only occasionally sends data, SSE + normal POST requests is usually simpler.

How Each One Works

Side-by-Side Comparison

Code: SSE

Server (Node.js / Express):

app.get("/events", (req, res) => {
  res.set({
    "Content-Type": "text/event-stream",
    "Cache-Control": "no-cache",
    Connection: "keep-alive",
  });
  const timer = setInterval(() => {
    res.write(`data: ${JSON.stringify({ time: Date.now() })}\n\n`);
  }, 1000);
  req.on("close", () => clearInterval(timer));
});

Browser:

const source = new EventSource("/events");
source.onmessage = (e) => console.log(JSON.parse(e.data));
// reconnects automatically if the connection drops

Code: WebSocket

Server (Node.js with the ws library):

import { WebSocketServer } from "ws";

const wss = new WebSocketServer({ port: 8080 });
wss.on("connection", (socket) => {
  socket.on("message", (msg) => {
    for (const client of wss.clients) client.send(msg.toString()); // broadcast
  });
});

Browser:

const ws = new WebSocket("wss://example.com:8080");
ws.onmessage = (e) => console.log(e.data);
ws.onopen = () => ws.send("hello");
// no auto-reconnect: handle ws.onclose yourself

Why AI Chat Apps Use SSE

When you ask Claude or ChatGPT a question, the answer appears word by word. The Anthropic and OpenAI APIs deliver this with SSE: the client sends one normal request, and the server streams tokens back as events.

It fits perfectly: the conversation is request → long one-way response. There's no need for a two-way socket, and SSE works through standard HTTP load balancers and CDNs.

Scaling Either One

Both keep a connection open per user, so the challenges are similar:

• Many open connections per server: use async servers (Node.js, Go, Python asyncio).
• Load balancer timeouts: raise idle timeouts and send periodic heartbeats.
• Broadcasting across servers: a user on server 1 must receive an event produced on server 2, so servers subscribe to a shared pub/sub channel.
• Serverless limits: many serverless platforms cap request duration, which affects long-lived connections. Check your platform.

Frequently Asked Questions

Conclusion

SSE and WebSockets both push data in real time, but they suit different shapes of communication. Use SSE for one-way streams like notifications, dashboards and AI responses, with free reconnection and plain HTTP. Use WebSockets when both sides need to talk constantly. Either way, plan for many open connections and a pub/sub layer as you scale.

Sources

• MDN: Using server-sent events
• MDN: The WebSocket API
• Anthropic docs: Streaming messages
• RFC 6455: The WebSocket Protocol

Last verified: 14 October 2026.

Related reads: WhatsApp System Design · How Figma's Multiplayer Works · Load Balancer Explained · Claude API Pricing

I write about building products and how real systems work. Follow on LinkedIn or X, or invite me to speak.