If you tested your blog’s performance on Google PageSpeed Insights yesterday and do so again today, you might be in for a surprise with a lower score even if not one byte (letter) got changed on your site. The reason: Google updated PageSpeed Insights to Lighthouse 6, which changes the KPI’s (the lab data metrics) that are reported, adds new opportunities and recommendations and changes the way the total score is calculated.
So all starts with the changed KPI’s in the lab metrics really; whereas up until yesterday First Contentful Paint, Speed Index, Time to Interactive, First Meaningful Paint, First CPU Idle and First input delay were measured, the last 3 ones are now not shown any more, having been replaced by:
- Largest Contentful Paint marks the point when the page’s main content has likely loaded, this can generally be improved upon by removing removing render-blocking resources (JS/ CSS), optimizing images, …
- Cumulative Layout Shift which measures unexpected layout shifts
The total score is calculated based on all 6 metrics, but the weight of the 3 “old” ones (FCP, SI, TTI) is significantly lowered (from 80 to 45%) and the new LCP & TBT account for a whopping 50% of your score (CLS is only 5%).
- GPSI already listed unused CSS, but now adds unused JS to that list, which will prove to be equally hard to control in WordPress as JS like CSS is added by almost each and every plugin. Obviously if you’re using Autoptimize this will flag the Autoptimized JS, disalbe Autoptimize for the test by adding ?ao_noptimize=1 to the URL to see what original JS is unused.
- GPSI now warns about using document.write and about the impact of passive listeners on scrolling performance which can lead to Google complaining about … Google :-)