Glossary · Speed and HTTP
Time to first byte
Time to first byte (TTFB) is the time from a request until the first byte of the response arrives. It covers connection setup, the request’s trip to the server and the server’s processing before it starts answering.
TTFB shows how quickly the server starts answering, before anything is downloaded or rendered. A high TTFB delays everything after it, including Largest Contentful Paint.
Google’s guidance is a TTFB of 0.8 seconds or less at the 75th percentile of visits. The usual causes of a slow one are pages built from scratch on every request, slow database queries, cold starts, redirects and long distances to the server; page caching and a CDN usually help most.
Tools measure it differently. Browsers count from the start of navigation, including redirects, DNS, connect and TLS; some monitoring tools report only the server’s wait after the request was sent. Compare numbers from the same tool.
Uptimecheck’s response time breakdown shows the server phase, the wait for the first byte after the request was sent, apart from DNS, connect and TLS. Page speed monitoring adds TTFB from a daily Google Lighthouse test and, for pages with enough visits, what real Chrome users experienced.
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Read0.8 seconds or less at the 75th percentile of visits, by Google’s guidance. Cached pages served from nearby can answer much faster.
Not directly; it isn’t one of the Core Web Vitals. It delays Largest Contentful Paint, which is.
Usually caching: the first request after a cached page expires is built from scratch. Cold starts on serverless platforms and busy databases do the same.
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