Free PageSpeed & Core Web Vitals Checker
Enter any page URL to measure it with Google Lighthouse — the 0–100 performance score plus Core Web Vitals (LCP, CLS, TBT) on mobile or desktop. Instant, free, no signup. Then let Merlonix track your pages and alert you when a metric slips.
What are Core Web Vitals?
Core Web Vitals are the three user-experience metrics Google uses as a page-experience ranking signal: Largest Contentful Paint (LCP — how quickly the main content renders), Cumulative Layout Shift (CLS — how much the layout jumps around while loading), and interaction responsiveness (Interaction to Next Paint, or INP; in a lab test its closest proxy is Total Blocking Time, TBT). This tool reports LCP, CLS, and TBT, plus First Contentful Paint and Time to First Byte, with Google's official good / needs-improvement / poor bands.
How is this different from Google PageSpeed Insights?
It runs the same underlying engine — Google Lighthouse, via the PageSpeed Insights API — so the score and lab metrics match. The difference is what happens after: PageSpeed Insights gives you one measurement when you click. Merlonix re-measures your pages on a schedule and alerts you the moment a metric crosses into "poor", so a performance regression from a new script, image, or deploy is caught in time rather than discovered weeks later in your rankings.
What is a good performance score?
The Lighthouse performance score runs 0–100. 90–100 is fast (green), 50–89 needs work (orange), and below 50 is slow (red). The score is a weighted blend of the lab metrics — LCP, TBT, CLS, and a few others — so a single heavy metric can pull it down. Mobile scores are usually lower than desktop because the test throttles CPU and network to model a mid-range phone; that is why this tool lets you switch between mobile and desktop.
Why does the score change between runs?
Lab measurements have run-to-run variance: a CDN cache-miss, a slow third-party script that loads on one run and not another, or normal network jitter can move the score a few points. That is exactly why a single measurement is a weak signal for whether your site is actually getting slower. A trend line — the same page measured repeatedly over days — is what separates real regression from noise, and continuous monitoring is what produces that trend.
How do I keep my pages fast over time?
Performance decays silently. A marketing team adds a heavier hero image; an analytics or ad tag is added; a dependency update ships more JavaScript; a deploy changes server response time. None of these throw an error — the page just gets slower, and it stays slower until rankings or conversions drop enough to notice. Claim the free Merlonix plan ($0, no credit card) to monitor a few pages continuously, or start a trial to track your whole site. Merlonix re-measures on a schedule and alerts you when a Core Web Vital crosses the "poor" threshold.
Related reading
Track PageSpeed & Core Web Vitals continuously
This free check measures one page today. Merlonix re-measures your pages on a schedule, tracks the score and Core Web Vitals over time, and alerts you the moment a metric crosses into “poor” — so you fix a regression before Google or your customers feel it.
No credit card required.