Quick Answer

REST is for request-response: CRUD operations, fetching data, submitting forms. WebSocket is for persistent streaming: live updates, notifications, collaborative editing. Don’t poll REST endpoints for real-time data — it wastes bandwidth and adds seconds of latency. They solve different problems, and most applications need both.

REST and WebSocket serve different jobs

REST and WebSocket are not competing technologies in the way that, say, REST and GraphQL compete. They solve fundamentally different problems.

REST gives you a stateless request-response model. The client asks for something, the server responds, and the connection is done. This maps cleanly to CRUD operations, public APIs, and any workflow where the client drives the interaction. REST benefits from caching, CDNs, and decades of tooling.

WebSocket gives you a persistent, bidirectional channel. Either side can send data at any time without the other asking. This is what you need when the server has new information and needs to push it to the client immediately — live scores, chat messages, stock prices, collaborative edits.

The mistake people make is trying to force one into the other’s territory.

When REST is the right choice

Most of your application should use REST (or standard HTTP). Specifically:

• CRUD operations — creating, reading, updating, and deleting resources. A user profile, a blog post, a payment transaction. Request-response is the natural model.
• Stateless queries — search results, filtered lists, paginated data. Each request is independent.
• Cacheable data — REST responses can be cached at every layer: browser, CDN, proxy, server. WebSocket data cannot.
• Public APIs — REST’s self-describing URLs, standard HTTP methods, and status codes make APIs discoverable and debuggable. Every HTTP tool works with them.
• File uploads and downloads — HTTP handles large payloads, range requests, and resumable transfers natively.

REST is not going away. Even applications with heavy real-time requirements still use REST for initial page loads, authentication, and configuration. The question is not “REST or WebSocket?” — it is “which parts of my application need each?”

When WebSocket is the right choice

Use WebSocket when the server needs to send data to the client without being asked:

• Live data feeds — sports scores, stock prices, sensor readings. The data changes on the server’s schedule, not the client’s.
• Chat and messaging — both sides send messages unpredictably. Request-response cannot model this without polling.
• Collaborative editing — multiple users changing the same document. Every keystroke from one user needs to reach all others within milliseconds.
• Notifications — a new order, a deployment failure, a teammate coming online. The server knows before the client.
• Multiplayer games — player positions, game state, actions. Latency is measured in single-digit milliseconds.

The common thread: data flows from server to client (or both directions) at unpredictable times, and latency matters.

The polling anti-pattern

The most common mistake in web architecture is polling a REST endpoint for real-time updates. A client sends GET requests every few seconds, hoping something changed. Usually, nothing did.

This is shockingly wasteful. When Ably analyzed Google’s implementation of live sports scores, the numbers were stark:

Metric	HTTP Polling	WebSocket
Total overhead (5 min)	68 KiB	852 bytes
Average latency	~5,000 ms	~200 ms
Data from server (5 min)	282 KiB	426 bytes (with deltas)
Overhead ratio	80x worse	Baseline

Google was sending the entire state object every 10 seconds, even when only 10 bytes had changed. That is a 3,200x data overhead on the actual payload delta.

Companies do this because REST is familiar and WebSocket feels hard. But that intuition is wrong. A WebSocket connection that receives pushed updates is simpler to maintain than a polling loop with retry logic, deduplication, error handling, and backoff. The polling loop has more failure modes, more code, and worse results.

If you find yourself writing setInterval(() => fetch(...), stop. You are building a worse version of what WebSocket gives you for free.

The signalling half-measure

A pattern that is better than polling but still suboptimal: using WebSocket solely to notify clients that something changed, then fetching the actual data via REST.

// The signalling pattern: WS notifies, REST delivers
const ws = new WebSocket('wss://api.example.com/notifications');

ws.onmessage = async (event) => {
  const signal = JSON.parse(event.data);
  // WebSocket only says "something changed"
  // Actual data still comes via REST
  const response = await fetch(`/api/orders/${signal.orderId}`);
  const order = await response.json();
  updateUI(order);
};

This eliminates polling latency — the client learns about changes instantly. But it doubles the round trips: one WebSocket message to notify, one HTTP request to fetch. For every update.

When signalling makes sense:

• The payload is large (images, documents, big JSON) and benefits from HTTP caching, CDN delivery, or range requests
• You have an existing REST API you cannot change and need to layer real-time on top
• The update frequency is low (a few per minute), so the extra round trip is negligible

When signalling wastes effort:

• The update payload is small (a score change, a status flag, a price tick) — just send the data over the WebSocket directly
• Updates are frequent (multiple per second) — two network round trips per update adds up fast
• You control both client and server and can design the WebSocket message format from scratch

If the data fits in a WebSocket frame (and almost all notification payloads do), send it directly. Skip the intermediate REST call.

The middle ground: SSE and HTTP streaming

REST and WebSocket are not the only options. Server-Sent Events (SSE) and HTTP streaming sit between them.

SSE uses a standard HTTP connection to stream events from server to client. It auto-reconnects on failure, supports event IDs for resumption, and works through proxies and CDNs that would buffer or block WebSocket upgrades. The trade-off: SSE is unidirectional. The client can only receive, not send.

For use cases where the server pushes and the client listens — live dashboards, notification feeds, log streaming — SSE is often good enough. It requires no special infrastructure, no WebSocket library, and no protocol upgrade. The browser’s EventSource API handles everything, including reconnection.

HTTP/2 streaming allows multiplexing many streams over a single connection, which helps SSE overcome the old HTTP/1.1 six-connection limit. However, true bidirectional streaming in the browser remains limited — the Fetch API’s ReadableStream is read-only.

Be honest with yourself about whether your use case actually needs bidirectional communication. If the server is doing all the talking, SSE is simpler to deploy, simpler to debug, and works in more network environments. See the WebSocket vs SSE comparison for a deeper dive.

Comparison table

Feature	REST (HTTP)	WebSocket	SSE
Connection model	Request-response	Persistent bidirectional	Persistent server-to-client
Data direction	Client-initiated	Both directions	Server to client only
Per-message overhead	500-2,000 bytes (headers)	2-14 bytes (frame)	~50 bytes (event fields)
Latency	Network round trip per request	Sub-millisecond after connect	Sub-millisecond after connect
Browser support	100%	99%+	97%
Proxy/CDN support	Excellent	Good (modern infra)	Excellent
Caching	Built-in (HTTP cache)	Not applicable	Not applicable
Auto-reconnection	Not applicable	Manual implementation	Built-in
Binary data	Via content types	Native support	Text only (base64 for binary)
Best for	CRUD, APIs, cacheable data	Chat, gaming, collaboration	Feeds, dashboards, notifications

Frequently Asked Questions

What is the difference between WebSocket and REST?

REST uses HTTP’s request-response model: the client sends a request, the server returns a response, and the exchange is complete. Every interaction is client-initiated and stateless — the server holds no memory of previous requests.

WebSocket starts with an HTTP upgrade handshake, then switches to a persistent full-duplex channel. Both client and server can send data at any time with minimal framing overhead (2-14 bytes vs hundreds of bytes for HTTP headers). The connection is stateful and stays open until explicitly closed.

The practical difference: with REST, the client must ask for data. With WebSocket, the server can push it the moment it is available.

Should I replace my REST API with WebSockets?

Almost certainly not. REST handles request-response workflows better than WebSocket ever will. It is stateless (easy to scale), cacheable (browsers, CDNs, and proxies all understand HTTP caching), and universally supported by every tool, library, and framework in existence.

Use WebSocket alongside REST, not instead of it. Let REST handle reads, writes, authentication, and configuration. Let WebSocket handle the live data stream. Most production applications use both.

Why is polling a REST API bad for real-time updates?

Three reasons. First, bandwidth: every poll sends full HTTP headers (500-2,000 bytes) whether or not anything changed. Over thousands of clients, this multiplies fast. Second, latency: if you poll every 5 seconds, your average delay is 2.5 seconds — an eternity for live data. Third, wasted computation: every poll hits your server, forces it to query data, serialize a response, and send it back, even when the answer is “nothing new.” Benchmarks show this pattern produces 80x more overhead than a WebSocket connection.

Can I use Server-Sent Events instead of WebSocket?

Yes, and you should consider it. SSE is simpler to implement, reconnects automatically, and works over standard HTTP without special proxy or load balancer configuration. If your data flows in one direction — server to client — SSE avoids the complexity of WebSocket.

The limitation is directionality. If the client needs to send data back to the server during the session (typing indicators, cursor positions, game inputs), SSE cannot do that over the same connection. You would need a separate HTTP request for each client-to-server message, which defeats the purpose at high frequency. In that case, use WebSocket.

What is the WebSocket signalling pattern?

Signalling uses a WebSocket connection to deliver instant “something changed” notifications to clients, which then fetch the updated data via a standard REST call. It replaces polling (the client learns about changes in milliseconds, not seconds) but still requires two network operations per update: the WebSocket notification and the REST fetch.

This makes sense when the payloads are large and benefit from HTTP caching, or when you are retrofitting real-time onto an existing REST API. It does not make sense for small, frequent updates (scores, prices, status flags) where you should send the data directly over the WebSocket connection.

Related Content

• WebSocket vs HTTP — how WebSocket compares to traditional HTTP request-response
• WebSocket vs SSE — when server-push over HTTP is enough
• WebSocket vs Long Polling — why WebSocket replaced Comet-style polling
• The Road to WebSockets — how HTTP polling evolved into the WebSocket protocol
• Protocol Decision Guide — choose the right protocol for your use case

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Written by Matthew O’Riordan, Co-founder & CEO of Ably, with experience building real-time systems reaching 2 billion+ devices monthly.