Glossary · Definition
TTFB (Time to First Byte)
TTFB (Time to First Byte) is the time from when the browser sends a request until it receives the first byte of the server's response. Measures backend + network latency, not rendering speed.
Definition
TTFB (Time to First Byte) is the time from when the browser sends a request until it receives the first byte of the server's response. Measures backend + network latency, not rendering speed.
What it means
Includes: DNS lookup + TCP handshake + TLS handshake + server processing + first byte sent. Google's Core Web Vitals indirectly cares about TTFB (it's the floor for LCP). Good TTFB: under 200ms (excellent), under 600ms (acceptable), over 1.5s (poor). Improved by: CDN caching, server-side rendering optimization, database query tuning, edge functions, geographic distribution of servers.
Advertisement
Why it matters
TTFB is the foundation under all other web performance metrics. If your TTFB is 1500ms, your LCP can't be better than 1500ms regardless of how fast your assets are. Many performance issues that look like 'slow rendering' are actually slow TTFB.
Frequently asked questions
How do I measure?
Chrome DevTools Network panel. Or PageSpeed Insights. Real-user monitoring (RUM) with WebPageTest, Cloudflare Analytics, or Vercel Analytics gives field data.
How do I lower it?
CDN edge caching (biggest win), database query optimization, lighter middleware, geographic origin shielding.