Core Web Vitals test
Check LCP, INP, and CLS across your site, plus the performance rules that actually move them.
Want to see the output first? See a sample report.
Core Web Vitals are Google's three user-experience metrics: Largest Contentful Paint (LCP) for loading, Interaction to Next Paint (INP) for responsiveness, and Cumulative Layout Shift (CLS) for visual stability. A single slow or janky page can drag down how your site feels and how it ranks.
squirrelscan audits the performance rules behind those metrics across every page it crawls: render-blocking resources, oversized images, missing dimensions, layout shift culprits, and more. You get a list of what to fix, ranked by impact.
What we check
Largest Contentful Paint (LCP)
The load time of the biggest element in view. We flag render-blocking CSS and JS, unoptimized hero images, and slow server responses that push LCP past the 2.5s threshold.
Interaction to Next Paint (INP)
How quickly the page responds to taps and clicks. We surface heavy scripts and long tasks that keep INP above the 200ms good bar.
Cumulative Layout Shift (CLS)
How much the layout jumps as it loads. We flag images and embeds without dimensions, injected banners, and late-loading fonts that push content around past the 0.1 threshold.
The rules behind the score
Every finding maps to a concrete rule with a fix, so you're not left staring at a number wondering what to change.
Why site-wide beats a single page
A lab test scores one URL under one simulated connection. That is useful, but your slowest pages are rarely your homepage. squirrelscan checks performance rules across the pages it crawls, so a bloated template or a heavy third-party script shows up everywhere it hurts, not just on the page you happened to test.
Lab data and field data are different things, and we're honest about it. Our audit measures the rules and lab signals you can fix in code. For real-world field data from Chrome users, pair it with Google's PageSpeed Insights.
Keep going
What LCP, INP, and CLS mean and how to move them.
A Lighthouse alternative for whole sitesWhy site-wide beats testing one URL at a time.
PageSpeed Insights (field data)Google's tool for real-world Chrome UX field data.
Frequently asked questions
- Is this lab data or field data?
- squirrelscan audits the performance rules and lab signals behind Core Web Vitals, the things you can fix in code. For field data measured from real Chrome users, use Google's PageSpeed Insights alongside it.
- What are good Core Web Vitals scores?
- Google considers LCP good at 2.5 seconds or less, INP good at 200 milliseconds or less, and CLS good at 0.1 or less. Each metric also has a 'needs improvement' and 'poor' band above those.
- Does it test every page?
- A cloud audit checks performance rules across the pages it crawls, so template-level issues show up everywhere they occur, not just on the URL you enter.
Run a full audit
This check is one of 249+ rules squirrel runs across your site. Sign up to run a full cloud audit, or install the CLI and audit locally for free.