Time to First Byte (TTFB)

The time between a browser requesting a page and receiving the first byte of a response from the server.

TTFB measures server responsiveness. It is not a Core Web Vital but it directly affects LCP — a slow server delays every subsequent metric. A good TTFB is under 800ms; below 200ms is excellent. TTFB includes DNS resolution time, TCP connection time, TLS handshake time, and actual server processing time.

High TTFB causes include: slow hosting/server hardware, database query bottlenecks, server-side rendering without caching, no CDN (geographic distance to server), and misconfigured server software. Fixes: move to faster hosting, implement server-side caching (Redis, Varnish), use a CDN for edge caching, optimise database queries, and pre-render pages where possible (SSG, ISR).

Note: TTFB for cached CDN responses is typically 10–50ms. For dynamic SSR pages without caching, 500–1500ms is common. Google's threshold for "good" TTFB in the Page Experience documentation is ≤800ms.