Time to First Byte (TTFB)
Time to First Byte (TTFB) is a metric that measures the duration between a user's HTTP request and the first byte of the server's response reaching the browser.
TTFB includes DNS lookup, TCP connection, TLS negotiation, and server processing time. Google considers TTFB good under 800ms. While not a Core Web Vital itself, TTFB directly impacts LCP — a slow server response delays everything that follows.
Common causes of high TTFB: slow database queries, unoptimized server-side rendering, missing CDN, distant server location, and cold starts on serverless platforms. On Vercel, cold starts can spike TTFB for infrequently accessed pages.
Optimize TTFB by using a CDN (Vercel Edge Network handles this), caching server responses where possible, optimizing database queries, using ISR or SSG for pages that do not need real-time data, and keeping serverless functions warm for critical paths.
Related terms
Largest Contentful Paint (LCP)
Largest Contentful Paint (LCP) is a Core Web Vital metric that measures the time from when the page starts loading to when the largest text block or image element is rendered in the viewport.
Page Speed
Page speed is the measurement of how quickly a web page's content loads and becomes interactive, typically measured by metrics like Time to First Byte (TTFB), First Contentful Paint (FCP), and Largest Contentful Paint (LCP).
Core Web Vitals
Core Web Vitals are a set of three Google metrics — Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS) — that measure real-world user experience.
First Contentful Paint (FCP)
First Contentful Paint (FCP) is a performance metric that measures the time from when the page starts loading to when any part of the page's content (text, image, SVG, or canvas element) is rendered on screen.
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