LCP — Largest Contentful Paint
How long until the main content is visible. Google treats 2.5s as good and anything past 4s as poor. Usually an oversized hero image, a slow server response, or a render-blocking font.
Find out which pages are costing you visitors
Google Lighthouse across your whole site, not just the homepage. Core Web Vitals per page, on mobile and desktop, with the specific fixes that move each metric.
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What the scan measures
The three Core Web Vitals Google actually ranks on, plus the diagnostics that explain them.
CLS — Cumulative Layout Shift
How much the page jumps around while loading. The classic cause is images and ad slots with no reserved dimensions, and it is what makes people tap the wrong thing.
INP — Interaction to Next Paint
How long the page takes to visibly respond after a tap or click. It replaced First Input Delay in 2024 and it is the metric heavy JavaScript hurts most.
Render-blocking resources
Stylesheets and scripts in the critical path that delay first paint, with the size and estimated saving of each one.
Image weight and format
Images served larger than their display size, missing modern formats, and the payload you could drop without touching a single line of layout.
Mobile versus desktop
Both strategies in one run, because mobile is where the score usually collapses and where Google indexes from.
Why milliseconds show up in revenue
Speed is one of the few technical metrics with a direct, repeatedly measured line to conversion.
Slow pages lose the visitor before the page arrives
Bounce rate climbs steeply between one and five seconds of load time. The visitor never sees the offer you paid to put in front of them.
Core Web Vitals are a ranking signal
Page experience is part of how Google ranks pages. It will not outrank genuinely better content, but between two comparable pages it decides which one wins.
Your homepage is not the problem page
Homepages get optimised because that is what people test. Scanning the whole site is usually how teams discover their product and checkout pages are twice as slow.
How the scan works
Real Lighthouse runs, across as many pages as you want to cover.
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Pick a site or a single page
Whole-site mode reads your sitemap and tests the pages it finds. Single-page mode tests exactly the URL you paste.
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Lighthouse runs per page
Each page is measured with Google Lighthouse under mobile and desktop conditions, so you get both profiles rather than an average that hides the bad one.
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Compare pages side by side
Results land in one table sorted worst-first, with per-page vitals and the opportunities behind each score.
Speed questions
Lab data versus field data, why scores move between runs, and what to fix first.
Why does my score differ from PageSpeed Insights?
PageSpeed Insights shows you two things: lab data from a single Lighthouse run, and field data from real Chrome users over the previous 28 days. Our scan is lab data, measured from our own infrastructure. Lab numbers are reproducible and good for finding causes; field data reflects your actual visitors on their actual devices. Expect the two to differ, and treat the lab run as the diagnostic.
Why does the score change when I scan the same page twice?
Lighthouse scores are sensitive to network conditions, CDN cache state and server load at the moment of the run, so a few points of movement between runs is normal. Treat a single score as approximate and watch the trend. If a page swings by twenty points, that variance is itself a finding — usually an uncached origin or a slow third-party script.
Should I fix mobile or desktop first?
Mobile, almost always. Google indexes your site mobile-first, mobile hardware is slower, and mobile networks are less forgiving. A page that is fast on mobile is essentially always fast on desktop; the reverse is not true.
Which fix gives the biggest win?
For most sites it is images: serving them at display size in a modern format, with width and height set so nothing shifts. That usually improves LCP and CLS at once. After that it is removing render-blocking scripts and cutting third-party tags, which is what INP responds to.
Can I test a page that needs JavaScript to render?
Yes. Lighthouse drives a real browser, so client-rendered pages are measured as a visitor experiences them — including the cost of the JavaScript itself, which is the point.
How many pages can I test in one run?
The instant teaser covers three pages. Continuing the full scan covers up to 50 pages, which is enough to compare templates — a product page, a category page, a blog post and checkout — rather than guessing from the homepage alone.
Check the rest of your site health
Speed is one of five checks. Each runs on its own, or all of them together in one score.
Accessibility
Find the barriers that turn visitors away, and the compliance gaps that carry legal risk.
Broken Links
Dead ends frustrate visitors and quietly drain SEO. We crawl every page and flag every 404.
AI-Readiness
Check whether ChatGPT, Perplexity and Google AI Overviews can reach, read and quote your content.
Security
Passive checks on transport security, defensive headers and public exposure signals.
Monitoring
Know your site is down before your users tell you, and watch its health score over time.
Full Site Check
Run every check in one pass and get a single health score with the top three things to fix.