Time to First Byte (TTFB)
TL;DR
TTFB is how long the browser waits for the first byte of the page from the server. Good is 0.8 seconds or less at the 75th percentile; over 1.8 seconds is poor. Every other loading metric waits on it.
Explain Simply
You order at a counter and the cook has not started yet. TTFB is the time before the first plate comes out: nothing can be served before it.
Time to First Byte measures the time from the start of navigation to the first byte of the response. It includes redirects, the DNS lookup, connection and TLS setup, and the server's own work to build the page. Thresholds at the 75th percentile: good ≤0.8 s, needs improvement 0.8-1.8 s, poor >1.8 s.
TTFB is not a Core Web Vital (the Chrome UX Report still labels it experimental), but FCP and LCP cannot start before it, so a slow TTFB makes a good LCP hard to reach.
Common causes: slow database queries or uncached server rendering, a server far from the visitors, redirect chains, and no CDN. Fixes: cache full pages or fragments, serve from a CDN close to users, remove redirects, and keep the server and its database in the visitors' region.
⚡Why It Matters
A slow server delays everything after it. For a site whose visitors are in Vietnam, hosting far away can add hundreds of milliseconds to every page before a single byte arrives.
🔍How CiteStat Checks
CiteStat shows the real-user TTFB from the Chrome UX Report under the scan result, and measures the lab server response time with PageSpeed Insights.
CiteStat Score Impact
Field TTFB is shown, not scored. Lab server response time takes up to 2 points from the Performance category.
Fix Difficulty
Editor: N/A | Developer: Medium | AI Agent: Easy