The time between a request and the first byte of the response arriving from the server.
ID
SS-DF-037
Confidence
High · 86
Evidence
Strong
Updated
2026-07-08
Definition
The time between a request and the first byte of the response arriving from the server.
Time to First Byte (TTFB) measures how long the server takes to begin responding after a request, capturing DNS lookup, connection setup, request processing and initial server response. It is a foundational performance metric because a slow TTFB delays every subsequent step, including Largest Contentful Paint. Slow database queries, unoptimised back-end code, lack of caching and distant server locations are typical culprits, and a CDN or better hosting often helps.