WebSockets vs Server-Sent Events: Which Real-Time Option Should You Use?
In short: Use server-sent events when the server pushes text updates and the browser mostly listens — dashboards, notifications, logs, and AI token streams. Use WebSockets when the client must send often on the same connection — chat, collaborative editing, games. Send occasional user actions with normal HTTP next to an SSE stream. If updates are rare, polling is still simpler.
What this means for you
- The page only needs to receive updates → SSE (EventSource).
- Both sides talk constantly, or you need binary frames → WebSocket.
- Do not open a WebSocket because "real-time" sounds modern. Direction of traffic decides it.
"We need real-time" is not one protocol. Live order status, a chat box, and a partner webhook are three different shapes. This post is the browser case: how the page stays current. Server-to-server push versus pull is covered separately in webhooks vs polling.
What each option actually is
Server-sent events are an HTTP response that never finishes. MDN's SSE guide is explicit: it is a one-way connection, so the client cannot send events back on it. The browser uses EventSource. The server responds with Content-Type: text/event-stream and writes data: blocks separated by blank lines. The HTML standard defines EventSource so servers can push data to web pages over HTTP.
WebSockets start as HTTP, then upgrade. MDN's WebSocket API describes a two-way interactive session: the page can send messages and receive them without polling for a reply. Text and binary frames both fit. The standard WebSocket interface is widely supported. It does not apply stream backpressure — if messages arrive faster than you handle them, the client buffers them.
Decision framework
| Your situation | Lean toward |
|---|---|
| Dashboard, ticker, notification feed, log tail | SSE |
| AI or LLM tokens streaming into a chat UI | SSE (client posts prompts with normal HTTP) |
| User clicks or form posts are occasional | SSE plus ordinary HTTP requests |
| Chat where every participant types constantly | WebSocket |
| Collaborative cursors, multiplayer input, binary frames | WebSocket |
| Updates every half minute or less often | Polling |
| Another company's server should notify your server | Webhook, not a browser socket |
The question that collapses most debates: does the client need to send at the same cadence it receives? If yes, WebSocket. If the client only listens, or sends now and then, SSE plus HTTP is enough.
Why SSE is the default for "live" pages
- It is still HTTP. Cookies, proxies, and access logs behave like other requests. You can read a stream with normal HTTP tools.
- Reconnect is built in. MDN says that if the connection closes,
EventSourcerestarts it until you callclose(). The HTML standard agrees: clients reconnect when the connection is closed, and an HTTP 204 tells the client to stop. The stream'sidfield sets the last event id the client remembers, which is how a resume works. A WebSocket client has to implement reconnect and replay itself. - Text is the format you already have. JSON progress events, notification payloads, and token deltas are text. SSE is UTF-8 by design.
Keep-alives matter. MDN notes that a line starting with a colon is a comment, and servers use those comments so idle streams are not killed by proxies.
The SSE limit people hit in production
MDN warns that without HTTP/2, browsers cap open connections per browser and domain at a very low number (6). Six tabs each holding an SSE stream can block images and API calls to that same host. Over HTTP/2, the maximum number of simultaneous streams is negotiated; MDN says the default is 100. If you ship SSE, serve it on HTTP/2 (or HTTP/3) and do not open a stream per widget on the page.
Why WebSockets still earn their place
SSE cannot send the client's messages on that connection, and it cannot send binary frames. When both directions are continuous, a WebSocket is the honest model:
- Chat, presence, and typing indicators.
- Collaborative editing where every keystroke or cursor move is a message.
- Games or trading-style UIs where input and state share one channel.
- Binary payloads you do not want to base64 into an event stream.
The costs are operational. The connection is stateful: you handle upgrade support on proxies, sticky routing or a pub/sub backplane so any server can reach the right socket, and your own reconnect logic. MDN also notes that a page with an open WebSocket may be kept out of the back/forward cache, so close the socket when the user leaves.
A pattern that avoids a rewrite
- If the screen only displays server state, start with SSE.
- Post user actions to normal endpoints. Authenticate, log, and retry those like any other request. Emit the result on the stream.
- Move a channel to WebSockets only when bidirectional traffic or binary frames are a real requirement, not a guess.
- Leave partner and backend notifications on webhooks or queues. A browser socket is the wrong tool for "Stripe should tell our server."
How much connection capacity, backplane, and reconnect behavior you need depends on concurrent users and message rate. That scope is set during discovery, not by a fixed timeline in a blog post.
If you are adding live updates to a product, our web and app development work covers the UI and the API behind it. For the Node.js side of streams and sockets, see Node.js development.
Frequently asked questions
What is the difference between WebSockets and server-sent events?
Server-sent events are a one-way HTTP stream. The browser uses EventSource, the server responds with text/event-stream, and only the server sends events. WebSockets open a two-way session: after the handshake, both the browser and the server can send messages without polling. SSE is for server push. WebSockets are for interactive traffic in both directions.
When should you use server-sent events instead of WebSockets?
Use SSE when the browser mostly listens: live dashboards, notification feeds, build logs, progress updates, and token-by-token AI responses. The EventSource API reconnects if the connection drops, and user actions can stay on normal HTTP requests. You do not need a WebSocket just because the page should update without a refresh.
When should you use WebSockets instead of SSE?
Use WebSockets when the client sends frequently on the same connection as it receives: chat, multiplayer input, collaborative cursors, or binary frames. MDN describes the WebSocket API as a two-way interactive session so you can send messages and receive responses without polling. SSE cannot carry client messages or binary data on that stream.
Do server-sent events reconnect automatically?
Yes, in browsers. MDN notes that if the connection closes, EventSource restarts it unless you call close(). The HTML standard also says clients reconnect when the connection is closed, and a 204 No Content response tells the client to stop reconnecting. The stream's id field sets the last event id so the client can resume. WebSocket reconnect and replay are application code you write yourself.
Is this the same choice as webhooks vs polling?
No. Webhooks and polling are about server-to-server or client-pull updates, often between your backend and another company's API. SSE and WebSockets are browser (or app) connections that stay open so a page can update live. A product can use webhooks between services and SSE or WebSockets for the user's screen.
Sources
- MDN — Using server-sent events — SSE is one-way, uses text/event-stream and EventSource, reconnects by default, and has the HTTP/1.1 connection-limit warning.
- MDN — WebSocket API — WebSockets are a two-way session so the client can send and receive without polling.
- HTML Standard — Server-sent events — EventSource pushes data over HTTP; clients reconnect after the connection closes; HTTP 204 stops reconnection.
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Related reading
- gRPC vs REST: Which API Style Should You Use?REST exposes resources over HTTP with JSON — the default for browsers, public APIs, and third-party clients. gRPC is a remote-procedure-call system that uses Protocol Buffers and HTTP/2, with generated clients and built-in streaming. Prefer REST at the edge. Prefer gRPC for internal service-to-service calls when you own both sides and need a strict contract or streaming. Most products that need both keep REST outside and gRPC inside.
- JWT vs Session Authentication: Which Should Your App Use?Server-side sessions store a session ID in an HttpOnly cookie and look it up on every request — logout and bans take effect immediately. JWTs are signed, self-contained tokens the client sends back; the server verifies the signature without a session store. Prefer sessions for first-party browser apps. Prefer short-lived JWTs (plus server-stored refresh tokens) for mobile clients, public APIs, and microservices that cannot share a session store. Many products use both.
- Webhooks vs Polling: Which Integration Pattern Should You Use?Webhooks push event data to your server when something happens; polling asks an API on a schedule whether anything changed. Prefer webhooks for near-real-time reaction when you can expose a public HTTPS endpoint. Prefer polling when delay is acceptable, the provider has no webhooks, or you cannot accept inbound traffic. For payments and other high-stakes sync, use both: webhooks for speed and a reconciliation poll for correctness.