WebSockets vs Server-Sent Events
Compare WebSockets and Server-Sent Events (SSE) for real-time features: direction, reconnection, scaling, proxies, and which to choose for live updates, chat, or streaming.
Quick Answer
If the server only pushes — live feeds, notifications, progress, LLM token streams — Server-Sent Events are simpler, auto-reconnect out of the box, and ride plain HTTP through every proxy and CDN. If clients must talk back over the same channel — chat, games, collaborative editing — WebSockets' bidirectional socket is the right tool. Most apps that reflexively reach for WebSockets actually need SSE.
Reviewed by TechLogHub Engineering Team. Last updated October 13, 2026. Initial publication — reflects current browser and HTTP standards behavior.
| Feature | WebSockets | Server-Sent Events |
|---|---|---|
| Direction | Bidirectional (full duplex) | Server → client only |
| Transport | TCP socket after HTTP upgrade | Long-lived HTTP response |
| Reconnection | Manual (heartbeats + backoff) | Automatic, with event-ID resume |
| Binary Support | ||
| Proxy/CDN Friendliness | Occasional issues with upgrades | Excellent (plain HTTP) |
| Browser API | WebSocket | EventSource / fetch streams |
| Scaling Model | Sticky/stateful connections | Stateless-ish HTTP, easier |
| Overhead | Minimal per message | HTTP framing per event |
WebSockets
A full-duplex protocol: an HTTP request upgrades to a persistent TCP-level socket over which client and server exchange messages freely in both directions.
Pros
- True bidirectional messaging over one connection
- Low per-message overhead after handshake
- Binary frames supported natively
- The standard for chat, games, and collaborative apps
- Mature server libraries in every ecosystem
- Subprotocols allow structured higher-level protocols
Cons
- No automatic reconnection — you build heartbeat + backoff yourself
- Stateful connections complicate load balancing and scaling
- Some proxies/corporate networks mishandle upgrades
- Bypasses HTTP semantics: no caching, no standard auth headers mid-stream
Best For
Chat, multiplayer games, collaborative editing, trading interfaces — anywhere the client sends frequent messages over the same live channel.
Server-Sent Events
A one-way stream of events from server to browser over a plain long-lived HTTP response, with a built-in browser API (EventSource) that handles reconnection automatically.
Pros
- Plain HTTP — flows through proxies, load balancers, CDNs
- Automatic reconnection with Last-Event-ID resume built in
- Trivial to implement server-side (a streaming response)
- Works with standard HTTP auth, headers, and HTTP/2 multiplexing
- Perfect fit for LLM token streaming and live feeds
- Degrades gracefully — it's just a request
Cons
- Server-to-client only — client replies go over separate requests
- Text-only frames (binary must be encoded)
- Per-domain connection limits on HTTP/1.1 (solved by HTTP/2)
- EventSource API lacks custom headers (use fetch-based clients)
Best For
Notifications, dashboards, progress updates, activity feeds, and AI/LLM response streaming — any 'server talks, client listens' pattern.
The Direction Question Decides Almost Everything
Real-time features split cleanly by who talks. Dashboards, notification bells, live scores, deploy logs, and AI token streams are broadcast-shaped: the server produces, the client consumes, and the client's occasional actions are ordinary HTTP requests anyway. Modeling these with WebSockets buys you nothing except a harder operational story. Conversely, a chat room or multiplayer cursor sync sends client messages constantly; forcing those through separate POSTs adds latency and connection churn that a WebSocket eliminates. Classify your traffic honestly before choosing the technology.
Reconnection Is Where WebSocket Projects Bleed
The EventSource API reconnects automatically: the browser retries with exponential backoff and sends the Last-Event-ID header so your server can resume the stream without losing events. With WebSockets, all of that is your code — detecting dead connections needs ping/pong heartbeats (TCP won't tell you promptly), backoff needs implementing, and missed-message recovery needs a protocol you design. Production WebSocket codebases accumulate hundreds of lines of connection-babysitting that SSE users simply never write. Libraries help, but the operational complexity remains yours.
Infrastructure: Plain HTTP Is a Superpower
SSE is just a response that hasn't finished, so every proxy, load balancer, CDN edge, and auth middleware treats it like normal traffic — HTTP/2 even multiplexes many streams over one connection, erasing the old six-connection limit. WebSockets upgrade away from HTTP: load balancers need sticky sessions or a pub/sub backplane (Redis is the classic answer) so a message reaches a user connected to a different node, some corporate middleboxes still break upgrades, and observability tooling sees opaque frames instead of requests. None of this is prohibitive — the WebSocket ecosystem is mature — but it's real cost that broadcast-only apps needn't pay.
Why LLM Apps Standardized on SSE
Token-by-token streaming from AI APIs is the canonical modern SSE use case: the client asks once (a POST), the server streams a long response, and resumability plus proxy-friendliness matter more than upstream messaging. That's why the major AI providers stream completions as SSE rather than WebSockets. The pattern generalizes: request/response with a very long, incremental response is SSE territory. Save WebSockets for genuinely conversational protocols where both sides interleave messages on one connection.
Verdict
Ask one question: does the client need to send messages over the same live channel? If no — and for feeds, notifications, progress bars, and LLM streaming the answer is no — use SSE and enjoy automatic reconnection and boring HTTP infrastructure. If yes — chat, games, collaboration — use WebSockets and budget engineering time for reconnection, heartbeats, and stateful scaling. Mixing is legitimate: SSE down, plain POSTs up covers a surprising share of 'real-time' apps.