The Server-Timing HTTP response header is a web standard that allows servers to communicate backend performance metrics — such as database query time, cache hit status, and server-side rendering duration — directly to the browser in a structured format. Each metric is declared as a name optionally accompanied by a duration in milliseconds and a human-readable description, for example Server-Timing: db;dur=45.2, cache;desc="HIT". The data appears in the browser’s DevTools Network panel under the Timing tab and is accessible via JavaScript through the PerformanceServerTiming interface, allowing real user monitoring tools to collect backend latency as part of field data. For SEO and performance purposes, Server-Timing is invaluable during investigation of Time to First Byte issues because it separates CDN and origin server processing time from network latency, making it straightforward to identify whether a slow TTFB is caused by a slow origin, a cold cache, or a slow database query. The header is defined in the W3C Server Timing specification.