Largest Contentful Paint
A Core Web Vital measuring the render time of the largest image, video poster or text block visible in the viewport; good is 2.5 s or less…
TechnicalTTFB
Time to First Byte
The interval between a navigation request starting and the first byte of the response arriving; a foundational input to LCP and a signal of server and network health.
In full
TTFB includes redirect time, DNS lookup, TCP and TLS handshakes, and the server's own processing. It is not a Core Web Vital but caps how good LCP can be — web.dev suggests aiming for 800 ms or less. Improvements come from edge caching, reducing redirect hops, connection reuse, faster backends and early hints. High TTFB also depresses crawl rate because crawlers throttle slow hosts.
Example
Moving an origin-only WordPress site behind a CDN with full-page caching drops TTFB from 1.4 s to 180 ms.
Related terms
Content Delivery Network
A distributed network of edge servers that caches and serves content close to users, reducing latency and offloading the origin.
Cache-Control
The HTTP header governing how browsers, CDNs and proxies store and revalidate a response, using directives such as max-age, s-maxage and…
Redirect chain
A sequence of two or more redirects between the requested URL and the final destination; each hop adds latency and risks signals being lost.
Crawl rate limit
The maximum simultaneous connections and fetch frequency a crawler will use for a host, adjusted automatically based on server response…