- 85 of 200
- Performance & Core Web Vitals
- Asset Compression & Optimization
- Medium
Short answer: pages often download JavaScript they never run: code for other pages, features nobody opened, or third-party tools. It still costs download and processing time. Check 85 warns when PageSpeed estimates 50KB or more of unused JavaScript on the page.
What Crawl Audit checks
- Full report: Lighthouse's unused JavaScript audit. Pass if the total possible saving is under 50KB; warning at 50KB or more.
- Free check: without PageSpeed, Crawl Audit warns if the page loads more than 12 external scripts, as a sign that some is likely unused.
The 50KB total is Crawl Audit's own line. Lighthouse "flags every JavaScript file with more than 20 kibibytes of unused code".
What Google says
Lighthouse: "Unused JavaScript can slow down your page load speed".
On devmarde.com
On 3 October, PageSpeed estimated about 74 KiB of unused JavaScript on our homepage, so we'd get this warning in the full report. Our Total Blocking Time was 30ms (check 76), so it isn't blocking much, but it's still bytes every visitor downloads. Our homepage loads 15 scripts, so the free check warns too.
How to trim it
- Remove what you don't use: old tracking tags, chat widgets, plugins.
- Split code by page, so each page loads only its own. Next.js does this per route.
- Load features on demand: a map, a video player or a comments box can load when the visitor reaches it.
- Check third parties: they are often the biggest share, and you can't minify or split their code yourself (check 99).
Sources
- Chrome for Developers, Remove unused JavaScript, checked 3 October 2026.
See how your site does on every check.
Crawl Audit runs this check and 199 others on your domain. The full report is $7.89, one time. The free check on this site covers 25.