TTFB (Time to First Byte)

TTFB covers everything that happens before the browser receives any content: redirects, service worker start-up, DNS lookup, connection and TLS negotiation, and the time the server takes to produce the response. It is not a Core Web Vital itself, but it comes before every other loading metric, so a slow TTFB makes a good LCP hard to achieve.

web.dev suggests most sites should aim for a TTFB of 0.8 seconds or less as a rough guide. Common causes of slow TTFB include slow database queries, uncached pages rendered on every request, underpowered hosting, redirect chains, and visitors being far from the server.

Typical fixes are full-page caching, serving cached HTML from a CDN close to visitors, optimizing slow queries and plugins, upgrading hosting, and removing unnecessary redirects. Measure TTFB from real users where possible, because a test from one location near your server can look much better than visitors elsewhere experience.