Navigation Timing API

WPT measures several technical metrics. Some of them are directly calculated with the Navigation Timing API (exposed via performance.timing)

I want to understand how WPT metrics are calculated from Navigation Timing API.

I already know for example that:

  • Document Complete = loadEventStart - navigationStart
  • Load Event Start = loadEventStart - navigationStart
  • domContentLoadedEventStart = domContentLoadedEventStart - navigationStart

Can someone tell me if following metrics are calculated with Navigation Timing API, and if yes, how?

  • TTFB
  • domInteractive ?= domInteractive - navigationStart
  • domComplete ?= domComplete - navigationStart

Is there any documentation about how the metrics are being calculated exactly, except the docs from github and the book “Using WebPageTest”?