TTFB Checker

Time to First Byte (TTFB) measures navigation start to the first response byte. It includes redirects, applicable service worker startup, connection setup, and server work. Field guidance uses 800ms or less as good at the 75th percentile. This checker's lab server-response measurement excludes DNS and redirects, so it covers only part of navigation TTFB.

A slow document response can delay FCP and LCP. TTFB is a diagnostic metric, not a Core Web Vital or a direct component of the Lighthouse Performance score. Early Hints and streamed HTML can deliver response bytes before the full document. Measure the LCP breakdown after a change; TTFB and LCP improvements can differ.

Slow TTFB is typically caused by: slow server-side processing, database query delays, no server-side caching, distance between user and server (no CDN), unoptimized backend code, shared hosting resource limits, and cold starts on serverless functions.

To improve TTFB: use a CDN to serve content closer to users, implement server-side caching (Redis, Varnish), optimize database queries, use edge rendering or SSR at the edge, upgrade hosting infrastructure, enable HTTP/2 or HTTP/3, and reduce server-side processing complexity.

Origin TTFB is the aggregate across all pages on your domain from real Chrome users. URL TTFB is specific to a single page. Origin data has more samples and is more stable, while URL data shows page-specific performance but may have insufficient data for low-traffic pages.