WebSocket vs REST API
A REST API answers one request at a time: the client asks, the server responds, and the exchange ends. A WebSocket keeps a single connection open so either side can send a message whenever it has one. Use REST for discrete reads and writes, and a WebSocket when updates flow continuously in both directions.
How a REST API handles a request
REST is an architectural style, not a protocol. In practice it means the client sends an HTTP request to a URL, the server sends one response back, and the exchange is over. Nothing about the client is remembered between calls, so any request can go to any server behind a load balancer, and a GET can be cached by a CDN or a browser without either side coordinating.
That statelessness is what makes REST cheap to operate. Every request carries its own authentication, its own headers, and its own body, which is also its main cost: a few hundred bytes of headers ride along with every call, and the server cannot tell the client anything until the client asks.
How a WebSocket connection works
A WebSocket starts as an ordinary HTTP request carrying an Upgrade: websocket header and a Sec-WebSocket-Key. If the server agrees it replies with 101 Switching Protocols, and from that point the same TCP connection carries WebSocket frames instead of HTTP messages, in both directions, until one side closes it. The protocol is specified in RFC 6455, and wss:// is the TLS form.
After the handshake the per-message overhead collapses to a 2 to 14 byte frame header, with no cookies, no auth header, and no round trip to reopen anything. That is the real advantage: not that a WebSocket is faster per byte, but that the server can speak first. The costs are the mirror image. The connection is stateful, so a client that reconnects lands wherever the load balancer sends it and your servers need shared state or sticky routing. Idle connections get killed by proxies unless you send ping and pong frames. And nothing in the WebSocket layer retries a failed message, so delivery guarantees are yours to build.
Where each one fits
REST is the default for discrete reads and writes: creating a resource, fetching a record, running a search, calling a payment or storage API. It fits anywhere the client knows when it needs data and can wait for the answer, and it inherits caching, retries, and observability from the HTTP tooling you already run.
WebSockets earn their complexity when messages flow continuously in both directions and latency is visible to a human: chat, multiplayer game state, collaborative editing, live trading views, and devices that stream telemetry while accepting commands on the same connection. If traffic only runs one way, from server to client, that is a weaker case for WebSockets than it looks.
Choosing between WebSockets and REST
Ask what triggers the next message. If the client always knows when it needs data, REST is simpler to build, cache, and scale, because every request stands on its own. If the server is the side with news, REST forces the client into a polling loop, and webhooks vs API polling covers what that loop costs in latency and wasted requests.
Then check whether both directions are actually necessary. If traffic only flows server to client, server-sent events do that job over ordinary HTTP with far less to operate, and WebSocket vs SSE compares the two in detail. If both ends are servers rather than a browser and a server, neither protocol fits well: holding a socket open between backends ties up a connection that sits idle most of the time, which is why webhooks send one HTTP request per event instead. Our webhook vs WebSocket comparison goes deeper, and Svix delivers those events for you with retries, signatures, and delivery logs.
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Svix handles signing, retries, rate limiting, and delivery observability for the webhooks you send to your users, so your team can stay focused on your product.
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