Time to First Byte is the time from starting navigation until a browser receives the first response byte; it reflects network, connection, redirects, cache and server work.
What the waiting time includes
Time to First Byte (TTFB) measures how long a client waits for the beginning of an HTTP response. For a browser navigation, the measured interval can include redirects, DNS lookup, connection and TLS setup, network latency, cache handling and server processing.
A slow TTFB therefore does not identify one cause. A nearby cached response and a distant request that reaches the application can take different paths even when they use the same URL.
Locate the delay
Start with the document request in a browser waterfall. Check redirects and connection setup before attributing the remaining wait to the application. Where server timing or logs are available, compare them with what the browser measured.
Repeat the request from the same location and record whether it was a cache hit, cache miss or authenticated request. Compare equivalent cases: a warm cache should not be presented as an application improvement over an earlier cold request.
Change the responsible layer
A redirect chain calls for a shorter route; repeated backend work may call for caching or application changes; a connection delay needs a different investigation. Test the suspected cause and compare the same request conditions afterwards.
TTFB ends before the page finishes loading. Images, styles and JavaScript can still delay useful content or interaction after the response begins, so inspect those stages separately.