TTFB (Time to First Byte)

Time to First Byte is the elapsed time from the start of a navigation or resource fetch until the first byte of a response begins to arrive, as defined by the measurement source. For a page navigation it can include redirects, service-worker startup, cache lookup, DNS, connection and TLS setup, request transit, server and application work, and response transit. It is therefore broader than backend processing time alone.

Why it matters: Use field data to understand real visitors and lab traces to separate redirect, DNS, connection, TLS, request, server, cache, edge, and response phases. Compare the same URL, geography, device or network conditions, cache state, and measurement definition; some tools start from the final URL, exclude redirect time, or handle `103 Early Hints` differently. As a rough web.dev guide, most sites can aim for navigation TTFB at or below 0.8 seconds at the 75th percentile, but TTFB is not a Core Web Vital and the meaningful target is one that does not prevent good user-facing metrics. Fix the dominant phase: shorten redirects, improve cache and edge strategy, remove slow application or database work, reduce connection distance, and stream useful markup when appropriate. A high value does not by itself identify the server as the cause.