Lighthouse is a page auditing tool by Google that measures performance, accessibility, best practices, and SEO. It’s built into Chrome’s Developer Tools and is also available via command-line interface (CLI) and as a browser extension. Web developers use the tool to discover ways they can improve the speed and performance of their sites.
Lighthouse, along with PageSpeed Insights and AMP, are part of Google’s push to get sites to improve their user experience (UX), especially on mobile devices. Google gives AMP pages preference in the Google News Top Stories carousel on mobile devices, and they have made speed a ranking factor for mobile searches. These actions have forced SEOs, and subsequently, webmasters and web developers to take page performance more seriously. It’s also made them more dependent on the Lighthouse tool because it can determine if their page performance is good enough for Google.
New Lighthouse performance score formula
On May 19, 2020, Google announced Lighthouse 6.0. Most webmasters, web developers, and SEOs will likely see slightly different scores because Lighthouse 6.0 calculates them differently from before. Google changed how they determine the score by removing two metrics and adding three new ones.
This is how the score was weighted and determined in version 5 of Lighthouse.
And this is how the score is weighted and determined in version 6 of Lighthouse.
The three new metrics are:
- Largest Contentful Paint
- Reports the render time of the largest content element visible within the viewport.
- Total Blocking Time
- Measures the total amount of time that a page is blocked from responding to user input, such as mouse clicks, screen taps, or keyboard presses.
- Cumulative Layout Shift
- Measures the sum total of all individual layout shift scores for every unexpected layout shift that occurs during the entire lifespan of the page.
New metrics reflect what is important to Google
Shane Jones, Senior Developer and Co-founder of the web performance agency Under2, told Coywolf that “the weighting switch on the new metrics is a pretty big deal, and many sites can expect to see their scores lowered.” He added:
I think all of these metrics now push the importance of how a user sees a site while it loads. Things like layout shift can be frustrating if a user clicks an element, and then right before they click, the layout changes, and the user ends up somewhere else.
Lighthouse offers a transparent view of what Google is focused on and what they think is important. It would behoove webmasters, web developers, and SEOs to seriously consider the new shift in metrics and calculations, and to update how their sites perform accordingly. If they don’t, it may end up costing them visibility in mobile search results.