Browser Support 43 12 31 11 Source What is TTFB? TTFB is a metric that measures the time between the request for a resource and when the first byte of a response begins to arrive. A diagram of network request phases and their associated timings. TTFB measures the elapsed time between startTime and responseStart. TTFB is the sum of the following request phases: Redirect time Service worker startup time (if applicable) DNS lookup Connection and TLS negotiation Request, up until the point at which ...