Test your Core Web Vitals.
A live test powered by Google PageSpeed Insights. Enter any URL and get LCP, CLS, Total Blocking Time and the overall performance score, for mobile or desktop.
Getting a free Google API key (about 3 minutes)
The key is free, gives you 25,000 tests per day, and removes the rate limit failures entirely. You only need to do this once.
Site owners embedding this tool: set the SITE_KEY constant at the top of the script instead, and restrict the key by HTTP referrer to your own domain. Browser requests send a referrer, so the restriction works and the key is unusable elsewhere.
Live data, straight from Google.
Enter a public URL
The page must be reachable without a login. Google loads it in a simulated mobile or desktop environment and measures what happens.
Google runs Lighthouse
This is the same engine behind PageSpeed Insights. We request it directly from your browser, so nothing passes through our servers.
Fix the biggest metric first
LCP is usually where the money is. Oversized hero images, render-blocking scripts and slow server response are the three most common causes.
Speed is a ranking signal and a revenue one.
Core Web Vitals measure what a real visitor experiences: how fast the main content appears, how much the layout jumps around, and how quickly the page responds when tapped. Google uses them as a ranking signal, though content relevance still matters far more.
The commercial case is stronger than the SEO case. A slow page loses visitors before they see anything you wrote, and that is true regardless of where you rank. Improving load time tends to improve conversion at the same time, which is a rare combination.
There is an important distinction in what you are seeing here. This is lab data, measured in a controlled simulation. Google also collects field data from real Chrome users, and the two can disagree, usually because real users have slower devices and worse connections than the simulation assumes.
One connection worth drawing: heavy client-side JavaScript hurts both performance and AI visibility. Moving to server-side rendering commonly improves your LCP and makes your content readable to crawlers that do not execute scripts. One fix, two problems solved.
Core Web Vitals questions.
What are good Core Web Vitals scores?
Largest Contentful Paint should be 2.5 seconds or less, Cumulative Layout Shift 0.1 or less, and Interaction to Next Paint 200 milliseconds or less. This tool reports Total Blocking Time as a lab proxy for INP, because INP requires real user interaction to measure.
Why does my score change between tests?
Lab tests simulate a network and device, and there is natural variance in server response, third-party scripts and network conditions. Run the test a few times and look at the pattern rather than treating any single number as definitive.
What is the difference between lab and field data?
Lab data comes from a controlled simulation and is useful for debugging because it is reproducible. Field data comes from real Chrome users over a rolling period and reflects actual experience. Google uses field data for ranking, so treat lab results as a diagnostic tool rather than the final word.
Do I need a Google API key?
In practice, yes. Google allows anonymous requests only for occasional low-volume use, and because that quota is shared globally it is usually exhausted, which returns a 429 rate limit error. A free key from Google Cloud gives you 25,000 requests per day and 240 per minute, and takes about three minutes to create. Restrict it to the PageSpeed Insights API and to your own domain by HTTP referrer, because an unrestricted key can be used by anyone who finds it. Any key you enter here stays in your browser and is never transmitted to us.
What usually fixes a poor LCP?
In order of frequency: an oversized or unoptimised hero image, render-blocking CSS or JavaScript, slow server response time, and client-side rendering that delays content until scripts finish. Serving properly sized modern image formats and moving rendering to the server address most cases.
Slow scores we can fix.
Send us the URL and we will identify exactly what is holding your Core Web Vitals back, and whether the same cause is also hiding your content from AI crawlers.