TTFB
Time to First Byte
In one line
TTFB (Time to First Byte) measures how long it takes from a request being sent until the first byte of the response arrives — a foundational metric for server responsiveness and LCP work.
Going deeper
TTFB (Time to First Byte) measures from the moment a request leaves the client to when the first byte of the response comes back. It rolls up server processing, network round trip, DNS, TLS negotiation and hosting location into one number.
It is not a Core Web Vitals metric in itself, but it is the foundation under LCP. With a slow TTFB, no amount of front-end work will push LCP under the 800 ms band.
Common levers in practice: introduce caching (especially via a CDN), tune database queries and trim middleware. For SSR-heavy sites, page-level caching tends to be the single biggest unlock.
Related terms
FCP
FCP (First Contentful Paint) measures the moment any meaningful content — text or image — first appears on screen, used as a supporting page-speed metric alongside Core Web Vitals.
SEOCLS
CLS (Cumulative Layout Shift) is the Core Web Vitals metric for visual stability — it sums up how much page elements jump around unexpectedly while the page is loading.
SEOINP
INP (Interaction to Next Paint) is the Core Web Vitals metric that captures overall interaction responsiveness across a session — and it officially replaced FID in March 2024.
SEOCDN
A CDN (Content Delivery Network) caches your content on edge servers worldwide so users are served from a nearby node — directly improving TTFB, LCP and overall page speed.
SEOTechnical SEO
Technical SEO is the infrastructure-level work — crawling, indexing, rendering, speed, structured data — that makes a site readable and rankable for search engines in the first place.
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