Google Chrome announced a big change to Lighthouse 10, which sees the removal of the Time To Interactive (TI) score. Tests indicate that a majority of webpages will see an improvement to their performance scores, with more than half of webpages experiencing an improvement in scores by over 5 points.
Time To Interactive – TTI
The Time To Interactive score measures how long it takes for a page to become interactive for site visitors. The score is a multi-step calculation that measures the resource loading to determine when a user can do things like click a button or use the site navigation.
The reason Time To Interactive is removed is because other metrics, Largest Contentful Paint (LCP), Speed Index, and Total Blocking Time together are better measures of when a webpage feels loaded.
The Chrome blog post explained:
“Largest Contentful Paint (LCP) and Speed Index are usually better heuristics for a page’s contents feeling loaded than a count of active network requests. Total Blocking Time (TBT) meanwhile handles long tasks and main-thread availability more robustly, and while not a direct proxy, tends to correlate better with Core Web Vitals as measured in the field.”
Tests conducted on over 13 million webpages indicate that 90% of webpages will see improved scores and that 50% of webpages will see performance improvements of over 5 points.
The weighting of the Time To Interactive score has, since Lighthouse 8, gradually decreased. This allowed the increase in the weighting of other metrics so that TTI ultimately contributed less to the final scores.
The decision to slowly decrease the weighting was explained as evolving the page speed metrics to become more accurate.
A note in the documentation for Lighthouse 8 explained:
“As with all Lighthouse score updates, changes are made to reflect the latest in how to measure user-experience quality holistically and accurately, and to focus attention on key priorities.”
The Time To Interactive score will still be available in the Lighthouse JSON output, with the score weighted to zero.
When Will Lighthouse 10 Changes Arrive?
The changes to Google Lighthouse are available right now on PageSpeed Insights tool. The testing version of Chrome, named Canary, also has the new version of Lighthouse 10.
Lighthouse 10 will be available in Chrome 112, currently scheduled for release on March 29, 2023. The most current version of Chrome is 110.
Featured image by Shutterstock/Roman Samborskyi