Understanding real-time crypto prices is critical for developers building applications that rely on timely market data. The term 'real-time' is often used loosely by APIs and dashboards, claiming to deliver instant data or live updates. However, this marketing lingo can be misleading. Latency—the time from a price change to when it appears in your app—varies widely. For example, CoinPaprika REST for centralized exchanges can achieve sub-second latency, while DexPaprika REST for DEX prices faces a fundamental limitation due to blockchain confirmation times.

To measure freshness—how old the data is when you receive it—developers need to consider the polling interval and the API's inherent delay. A 5-second polling interval can result in data that is 7-8 seconds stale, as seen in the CoinPaprika example. In contrast, DexPaprika Streaming using Server-Sent Events (SSE) provides updates as they occur, reducing freshness to just 1-2 seconds. This approach is particularly useful for applications requiring frequent updates and a real-time user experience.

When choosing between polling and streaming, developers should consider their application's needs. Polling is simpler to implement and sufficient for infrequent updates, but it adds latency. Streaming, while more complex, offers lower freshness and is ideal for high-traffic applications monitoring multiple tokens. To verify an API's claims, developers should measure P50, P95, and P99 percentiles rather than relying on average latency statistics, which can be misleading. By running their own measurements, developers can ensure they are getting the performance they need.