Google kills off the Time To Interactive metric in Lighthouse 10

Google kills off the Time To Interactive metric in Lighthouse 10
Photo: Midjourney
Lasse Schou

Lasse Schou

13 February 2023

Google recently announced a new major version of their popular Lighthouse tool that's used by millions across the globe to check the performance and best practices of websites.

Lighthouse is also the software used by PageVitals to run hundreds of thousands of tests every day for our clients. Read more about Lighthouse in this article.

Bye bye, Time-to-interactive

The biggest change in the way Lighthouse scores the performance of websites is around the metric Time To Interactive (TTI).

The TTI metric was deprecated in Lighthouse 8 and is now being sunset completely.

TTI marks a point in time, but the way it's defined makes it overly sensitive to outlier network requests and long tasks. 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. Google announcement

The contribution that TTI made to the performance score has now been taken over by Cumulative Layout Shift (CLS) which now makes up 25% of the score.

Lighthouse Scoring Calculator, comparing version 9 and 10

As you can see from the illustration above, more emphasis has been put on Cumulative Layout Shift, and rightfully so. Websites with flickering content, confusing ads and links that jump up and down is a major browsing experience issue and should be avoided. Let's hope that Google's new scoring helps improve this.

Back/forward cache audit

A new audit is added that checks whether your page is optimized for the super fast Back/Forward cache (bfcache) or if your page is accidentally blocking it. The audit will check for things like unload or beforeunload handlers (should be avoided) and connections not having been closed properly.

Don't prevent paste in all input fields

Lighthouse earlier checked that your website doesn't prevent pasting content into password fields, but has now been expanded to check all non-readonly input fields. Preventing pasting is seen as a no-go both in terms of usability and security.

Try out Lighthouse 10 with PageVitals by end of March

At PageVitals we're working fast and we'll start using Lighthouse version 10 on March 29th, 2023. You may need to adjust your budgets and alerts after the change.

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