DNS & Glossary

TTFB (Time To First Byte)

How long from request to the first response byte — the sum of DNS, connection, TLS handshake and server processing time, and a key latency signal.

What it is

TTFB bundles several phases: DNS resolution, TCP (or QUIC) connection, TLS handshake, the request travelling to the server, server think-time, and the first byte travelling back. A high TTFB points at slow DNS, distant servers, or slow backend processing — a CDN and caching usually help.

Why it matters

  • It is an early, user-perceived latency signal and an input to Core Web Vitals.
  • It isolates network/setup cost from download time.

Common mistakes

  • Blaming TTFB solely on the server when DNS or TLS setup is the real cost.
  • Uncached, database-heavy responses inflating server think-time.

How WebInspect checks this

  • WebInspect measures TTFB alongside DNS, connection and TLS timings in its performance analysis.