TTFB (Time to First Byte) is the time between a browser requesting a page and receiving the first byte of the server's response.
TTFB captures everything that happens before content can even begin to load: DNS lookup, the connection and TLS handshake, the server processing the request, and the network trip back. A slow TTFB delays every visual milestone that follows, which is why it acts as an upstream influence on Largest Contentful Paint. It is a diagnostic metric rather than one of the three Core Web Vitals.
Google suggests aiming for a TTFB under roughly 800 milliseconds for most sites. Common causes of a high TTFB are slow server-side processing, unoptimized database queries, no caching, and distance between the user and the origin server. Fixes include page caching, a content delivery network to serve responses closer to users, faster hosting, and reducing expensive work on each request.
Related: LCP complete guide, Field vs lab data, URL Structure
Claude Vincent is a technical SEO consultant focused on crawlability, rendering, and AI-search visibility. He writes the field guides and case studies at SEO ProCheck, with a bias toward the durable, unglamorous work that decides whether search engines and AI answer engines can actually read and cite a site.
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