Google PageSpeed Insights updated, new metrics and recommendations!

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Paint, First CPU Idle and First input delay were measured, the last 3 ones are now not shown any more, having been replaced by: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, …
  • Total Blocking Time quantifies how non-interactive a page while loading, this is mainly impacted by Javascript (local and 3rd party) blocking the main thread, so improving that generally means ensuring there is less JS to execute
  • 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%).
Lastly some one very interesting opportunity and two recommendations I noticed;

  • 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 🙂

Summary: Google Pagespeed Insights changed a lot and it forces performance-aware users to stay on their toes. Especially sites with lots of (3rd party) JavaScript might want to reconsider some of the tools used.

8 thoughts on “Google PageSpeed Insights updated, new metrics and recommendations!”

  1. Currently working on a post about this and found this while Googling. 🙂 Good to see you share my visions. 😀
    I’m somewhat happy with the changes, though. Because it really pushes the bar when it comes to creating fast themes, which IMO only a handful of theme developers really seem to get. Lots of them just add a lot of crazy Special FX to their theme, because sexy sells.
    It is somewhat inherent to WordPress themes (and completely inherent to page builders) to contain a lot of unused JS, because the library should be loaded just in case you’re going to use it. But I hope that all developers now will start working on ways to optimize their plugins, e.g. only load libraries if a certain block is included on the page.
    One question, though: does Autoptimize already generate separate css files for each page types (e.g. post, page and homepage)? Because I noticed different CSS files being loaded, e.g. appended with _single.css.

    • AO just optimizes what it finds in the unoptimized HTML, so _single_ ones are excluded unminified files which AO then minifies. By default CSS in wp-content/uploads and wp-content/cache is excluded, which is typically where pagebuilders (yep, those again) store their page-specific CSS 🙂

  2. Hi Frank, I played around with the new pagespeed metrics and found that critical CSS and defer JS play a key role for success with the new metrics 🙂 Thank you for your awesome plugins

  3. My biggest problem now with the new page insights is that Autoptimize is now the problem. I have tried everything to address it.
    Three area’s of concern
    Remove unused JavaScript
    Does not use passive listeners to improve scrolling performance
    Reduce JavaScript execution time 3.0 s

    • well, Autoptimize simply aggregates all JS from your theme & plugins; all of these problems actually originate from the original JS. test your site with ?ao_noptimize=1 appended to the URL and compare results to see what the problem is.

  4. Frank,
    I just started using your Autoptimize plugin and got Critical CSS Shortpixel set up. My site is doing much better and I have you to thank for that. I am having some issues with mobile ranking dreadfully and I am looking into the causes.
    Thank you so much for your brilliant work!


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