Performance
TTFB
Time To First Byte
Time To First Byte (TTFB) measures how long after a request before the first byte of the response arrives. It captures DNS lookup, TCP/TLS handshake, request routing, and server processing — a comprehensive backend health signal.
In depth
TTFB is the floor for every other loading metric: LCP can never be better than TTFB plus the rendering time. A TTFB above 800 ms almost guarantees a poor LCP no matter how well you optimise the front end.
Factors that affect TTFB: origin server response time, distance to the user (mitigated by CDNs and edge rendering), database query speed, and SSR rendering cost. Measuring TTFB regionally exposes geographic gaps that an aggregate average hides.
Why it matters
TTFB is often the first thing to fix when LCP is bad. Caching at the edge, putting static HTML on a CDN, or moving to edge functions can cut TTFB from 1500 ms to under 200 ms — and pull LCP into the green automatically.
How Lemwatch helps with ttfb
Lemwatch monitors ttfb continuously and alerts you the moment something changes.
Performance monitoring →Related terms
LCP
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Core Web Vitals
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CDN
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Lighthouse
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Page Speed
Page speed is a colloquial term covering the time a page takes to become visually complete and interactive. It…
Browse the full Lemwatch monitoring glossary (47 terms).