mabl now supports tracking your page load performance in Chrome with the perceptual speed index metric. This metric describes how quickly the contents of a page are visibly loaded with an emphasis on user perception of loading speed. This metric is also used by the Google Lighthouse tools as the primary measure of page loading speed.
In addition to tracking individual page/URL loading speed like Lighthouse, mabl tracks the speed index for each step of a journey, even if there is no additional page load. This can be especially useful for monitoring performance of a single page app where pages are dynamically updated in response to user actions without changing the URL.
To view the speed index of a step in any Chrome journey run, select the step in the output view for the run and then select the "Performance" tab. This view shows the speed index for updating the page in response to the action in the highlighted step. In addition to the highlighted value for the journey run being viewed, the chart shows all recent runs of the same journey step (for the same journey version, plan, and environment).
Currently, the speed index is only available for runs in Chrome that have a screenshot and Chrome timeline trace. For more details on page loading performance, including each render event during the page update, you can download and view the Chrome timeline trace. An overview on how the speed index is calculated is available here. Specific details of the perceptual speed index variant used in mabl are available here and here.