GlossarySEO
What is Time to First Byte (TTFB)?
Also called: TTFB, server response time
Definition
Time to First Byte (TTFB) is the time from starting to navigate to a page until the first byte of the response arrives. It's not a Core Web Vital, but it delays everything after it, including LCP.
Time to First Byte (TTFB), explained
web.dev defines TTFB as the time between the start of navigation and when the first byte of the response begins to arrive. It includes redirect time, service worker startup, DNS lookup, connection and TLS negotiation, and the request itself up to the first response byte. So a slow TTFB can come from the network, from redirects, or from your server taking a long time to build the page.
web.dev's guidance says good TTFB is 0.8 seconds or less and poor is more than 1.8 seconds, at the 75th percentile. It also says TTFB is not a Core Web Vital, and that it isn't absolutely necessary to meet the good threshold as long as it doesn't stop you scoring well on the metrics that matter. In practice, though, a slow TTFB makes a good LCP hard, because nothing can render until the HTML arrives.
The common causes on startup stacks: pages rendered on every request with slow database or API calls, cold starts on serverless functions, redirect chains before the real page, and origins far from users with no CDN caching. For crawlers, slow responses also matter: Google's crawlers slow down when a site responds slowly.
The fixes: serve pages statically or cache rendered HTML at the edge, move slow data fetching off the critical path, collapse redirects, and put a CDN in front of the origin. web.dev also mentions 103 Early Hints, which lets the server tell the browser about critical resources before the full response is ready.
Why it matters for founders
TTFB is the first domino. If your server takes a second to respond, every other speed fix starts a second late, for users and for Googlebot.
Example
Your docs pages are rendered per request and query a CMS, giving 1.5s TTFB. You switch to static generation with revalidation on publish, and TTFB drops to under 200ms from the CDN.
Common mistakes
- Rendering static content on every request.
- Redirect hops before every page load.
- No CDN caching for HTML.
- Treating TTFB as a Core Web Vital and over-optimizing it.
Sources
Checked
Related terms
- Largest Contentful Paint (LCP)Largest Contentful Paint (LCP) is a Core Web Vital measuring how long it takes for the largest image or text block in the viewport to render. Google's target is 2.5 seconds or less for 75% of page loads.
- Static site generation (SSG)Static site generation (SSG) builds each page's HTML once, at build time, and serves the same file to every visitor. It's the fastest and most reliable way to give crawlers complete pages.
- Server-side rendering (SSR)Server-side rendering (SSR) means the server builds a page's full HTML for each request and sends it ready to display. Crawlers and users get content immediately, without waiting for JavaScript.
- Redirect chainA redirect chain is when a URL redirects to another URL that redirects again before reaching the final page. Each hop adds delay, and long chains or loops can stop crawlers from reaching the page.