TTFB (Time To First Byte) measures the elapsed time from when a browser sends a request to when it receives the first byte of the response. It captures DNS lookup, TCP and TLS handshakes, request travel time, server processing, and any CDN edge work. Google's guideline is to keep TTFB under 800 ms for a good experience.
Why it matters
TTFB is the floor for every other loading metric. A slow server response delays LCP, FCP, and the start of script execution, which feeds directly into Core Web Vitals. For users on high-latency networks the impact compounds across every navigation, and search crawlers see the same slowness when fetching pages.
How to fix
- Serve cacheable HTML and assets from a CDN so users connect to a nearby edge.
- Add full-page or fragment caching for dynamic content that does not change per user.
- Profile and tune slow database queries, N+1 loops, and synchronous external API calls.
- Enable HTTP/2 or HTTP/3 and modern TLS to cut handshake overhead.
- Turn on compression (gzip or Brotli) for HTML so the first byte arrives faster on slow links.
- Measure from multiple regions; web.dev documents current TTFB targets in its TTFB guide.