TTFB

TTFB (Time To First Byte) is the time between a browser sending a request and the first byte of the response arriving back. It is the headline server-side performance metric in web hosting, because it captures everything before any HTML even starts to download: DNS lookup, TLS handshake, network round-trip, server processing, database queries and any backend logic. A good TTFB is under 200ms for cached pages and under 500ms for dynamic ones; over 800ms is a warning sign that the server, the application or the network is too slow. TTFB feeds directly into Core Web Vitals (especially LCP) and is what Google measures when it talks about "slow servers".

How it works

TTFB is measured per request, from the moment the browser sends the request packet to the moment the first response byte arrives. It is reported by Chrome DevTools, WebPageTest, and the Web Vitals JS library, and it is one of the most actionable metrics a host can move.

Why it matters

High TTFB feels like a slow site even when the page eventually loads quickly, because nothing visible can happen until the first byte arrives. Lowering it is one of the highest-impact performance wins: pick a host closer to your audience, add a CDN, cache database queries, or precompute the response.

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Frequently Asked Questions