Definition

Time to First Byte (TTFB) is a performance metric that measures the time between a browser making a navigation request and receiving the first byte of the page's response from the server.

TTFB includes redirect time, service-worker startup, DNS lookup, connection negotiation (TCP and TLS), and the initial server response. web.dev's guidance is to aim for TTFB ≤0.8s at the 75th percentile of field data; values above 1.8s are considered poor. TTFB is a precursor to FCP and LCP — improvements in TTFB tend to flow through to those metrics, and slow TTFB makes "good" Core Web Vitals scores harder to achieve.

Examples

• Caching impact on TTFB

  A WordPress site without page caching takes 1.4s to begin sending HTML on each request. After enabling object caching and putting a CDN in front of the origin, TTFB drops to 280ms, with corresponding improvements visible in LCP and FCP in CrUX field data.

Sources

• web.dev — Time to First Byte (TTFB)

Related terms

• Largest Contentful Paint
  A Core Web Vitals metric measuring how long the largest visible content element on a page takes to render after loading begins.
• First Contentful Paint
  A web performance metric measuring the time from page load start to the first visible text, image, or non-blank canvas being rendered.
• Core Web Vitals
  A set of three Google metrics that measure real-world page experience: loading speed, interactivity and visual stability.

Where QueryCatch uses this

• Page Optimisation
• SEO Audit