Speed index is an application performance monitoring metric automatically calculated by mabl. It tracks the loading speed of page URLs and individual test steps, even without a page load. This makes it a helpful metric for single-page apps, where pages are dynamically updated in response to users actions without changing the URL.
mabl uses speed index to calculate cumulative app load time, a key metric for monitoring your app’s overall performance over time.
To review the speed index for an individual step, select the step in the test output, click the Logs tab, and then select the Performance tab. The highlighted value indicates the speed index of the current test run. The other points on the chart show the speed index for recent runs of the same test step for the same test version, plan, and environment.
Speed index chart
Speed index is available only for test runs in Chrome and Edge for steps with a screenshot and step trace.
Speed index and Google Lighthouse
Speed index is a key metric in the Google Lighthouse tools for measuring page loading speed. Note that currently Lighthouse tools do not track loading performance of UI interactions where the page URL doesn’t change.
Lowering the speed index
You can lower your speed index score by optimizing the application pages and screens to load visually faster. Some good resources on the topic are the articles on Optimizing Content Efficiency and Optimizing the Critical Rendering Path from the Google Developers network.