Time to First Byte (TTFB) measures the interval from starting a request until the first response byte arrives. It includes multiple parts of the request path, such as connection setup, network travel, and server processing, depending on how the measurement is taken.
Use TTFB to narrow a delay
Compare TTFB across repeated requests and note whether the connection was reused. A slow first request may reflect DNS, TLS, or connection setup; a slow response on a reused connection may point more toward server processing or network latency. TTFB alone does not identify the cause.
Measure with a consistent client and environment, and separate it from total download time. A response can have a low TTFB but a large body that takes much longer to transfer. For crawl scheduling, high latency may justify reducing concurrency to a host, but first confirm that the delay is persistent rather than a one-off.
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