Performance
Time to First Byte (TTFB)
The time from a visitor starting to load a page until the first byte of the server's response arrives, reflecting the connection, any redirects and server speed.
TTFB comes before everything else in a page load: however well optimized the images and scripts are, nothing can render until the first byte arrives. It includes redirects, the DNS lookup, connecting to the server and the server’s own processing time, so a slow server, a chain of redirects or a host far from the visitor all show up here.
Google’s web.dev guidance suggests aiming for 0.8 seconds or less and treats anything over 1.8 seconds as poor, while calling these thresholds a rough guide (web.dev). TTFB is not a Core Web Vital, but a slow one makes a good Largest Contentful Paint hard to reach.
On dynamic sites, a slow TTFB usually means uncached database queries, heavy plugins or slow calls to other services while the page is generated. Full-page caching helps. Serving prebuilt pages from a CDN removes most of that work at request time, which is why a move to static site generation usually improves TTFB.
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