How REST works
REST follows the same request-and-response model as most of the web. An application requests something specific, such as a snapshot for a symbol or a range of historical bars, the server responds once, and the exchange is complete. The approach is simple, cacheable, and straightforward to debug with standard HTTP tools. Its limitation is that a response reflects only the state at the moment of the request; learning what has changed requires another request.
How WebSocket works
A WebSocket connection is opened once and remains open. After subscribing to a set of symbols, the client receives each new update over the same connection as it occurs, without repeated requests. This suits live prices, where every change is relevant. The cost is an ongoing connection that must be maintained and reconnected if it drops, which requires more handling than a single request.
Why polling REST is unsuitable for live data
A common anti-pattern is calling a REST snapshot endpoint at short intervals to simulate a live feed. This wastes bandwidth on responses that often repeat, adds latency equal to the polling interval, and can quickly reach rate limits. Frequent polling for freshness is an indication that WebSocket is the appropriate transport, since it delivers each update as it occurs with less traffic and lower latency than polling can achieve.
Using both together
Production systems typically combine the two. The common pattern is to load the initial state over REST, including a current snapshot and a backfill of historical bars, then open a WebSocket to keep the data current. REST provides the starting state and the historical depth, while WebSocket maintains the live edge. One covers past data, the other covers ongoing updates.
REST and WebSocket on SiftingIO
SiftingIO provides both transports under one credential and one JSON schema. Snapshots, historical bars, fundamentals, and reference data are served over REST, while live ticks stream over WebSocket subject to per-tier connection and subscription limits. Because both use the same structures, a chart can be backfilled over REST and kept live over WebSocket without converting between formats. Enterprise customers can also receive the same aggregated prices over FIX.