Time to First Byte (TTFB)
Time to First Byte measures how long after a request the server sends the first byte of the response, an early speed signal that affects both crawl efficiency and how fast a page can load.
Also known as: TTFB
TTFB measures how fast your server starts responding. It's the time from a request to the first byte coming back — capturing server processing, database queries, and network latency before any rendering even begins. A slow TTFB delays everything downstream, including FCP and LCP.
For the access pillar, TTFB matters on both ends: crawlers fetching many pages are more efficient and thorough when your server responds quickly, and users get a faster start. The common improvements — caching, a CDN, and serving pre-rendered or static responses instead of computing each page on demand — reduce TTFB and make your content promptly available to bots and people alike.
Example. A static page served from a CDN can post a TTFB in the tens of milliseconds, while a slow app server doing heavy work per request might take a second or more before the first byte — delaying the crawler and the visitor before anything renders.
Relevant pillar
Related terms
- Core Web VitalsCore Web Vitals are Google's set of user-experience metrics for loading, interactivity, and visual stability, a measurable proxy for the page speed and quality that support AI visibility.
- First Contentful Paint (FCP)First Contentful Paint is a performance metric measuring how long after navigation the browser renders the first piece of page content, used as a proxy for how quickly a page becomes useful.
- Server-Side Rendering (SSR)Server-side rendering is when a web server generates a page's full HTML for each request and sends it ready-to-read, so content is present immediately for both browsers and AI crawlers.