Web.dev is Built on the Lighthouse Infrastructure in the Back-end
Google’s web.dev tool is built on Lighthouse in the back-end to maintain consistency with other tools.
Google Speed Tool Scores Don’t Map One-to-one with How Speed is Used for Rankings
The scores shown in Google’s page speed tools such as PageSpeed Insights don’t map one-to-one with how sites will be ranked in search in relation to their speed.
Pages With Long Download Times Reduce Googlebot’s Crawl Budget
If a page takes a long time to download then this will use up crawl budget for Googlebot, meaning it will have less time to crawl other pages on your site. Look at the ‘time spent downloading a page’ report in GSC to spot these issues.
Combine Separate CSS, JS & Tracking URLs to Increase Googlebot Requests to Your Server
To improve site speed and allow Googlebot to send requests to your server more frequently, reduce the number of external URLs that need to be loaded. For example, combine CSS files into one URL, or as few URLs as possible.
New PageSpeed Insights Tool Uses Lighthouse Data & Runs Lighthouse Audits
The new PageSpeed Insights tool runs Lighthouse audits for you using data from across different devices.
Inconsistency in PSI Alerts Suggests Being on the Edge of Google’s Speed Requirements
The PageSpeed Insights team try to maintain stable tests for websites, so if a site has fluctuations between getting alerts and passing the tests, this suggests the site is right on the edge of Google’s speed requirements.
Google Reassessing Use of Scores in Speed Testing
Google are reassessing their use of scores as part of testing tools, like PageSpeed Insights, as this can result in people focusing too much on addressing things that will improve their score rather than other areas which will have a bigger overall impact.
Testing Tools Can Incorrectly Show Scripts Aren’t Optimised
Testing tools, like PageSpeed Insights, can show that scripts such as Google Analytics or AdSense aren’t optimised because they are configured for specific browsers.
Page Speed Update Will Use Scale to Assess Speed
The Page Speed update will be on a scale where: the faster pages are, the more Google can take this into account. This approach is opposed to Google’s previous speed update, which only differentiated between very slow pages and all other pages.