Core Web Vitals sound technical, but they measure three simple things every visitor feels. How fast does the main content appear. Does the page jump around while loading. Does the page respond quickly when I tap something. Google uses these signals as part of its page experience ranking system, and visitors use them to decide whether to stay.
The three Core Web Vitals
- LCP, Largest Contentful Paint: how long it takes for the main content, often a hero image or headline, to appear. Good is under 2.5 seconds.
- CLS, Cumulative Layout Shift: how much the layout moves while loading. Good is under 0.1.
- INP, Interaction to Next Paint: how quickly the page responds to taps and clicks. Good is under 200 milliseconds. Lab tests often use Total Blocking Time as a close indicator.
What our checker shows
The Core Web Vitals Checker tests a page on mobile or desktop. When Google Lighthouse data is available it shows LCP, CLS, TBT, FCP, Speed Index and Time to Interactive, plus real user field data when Google has it. It always runs our own live performance checks for server response, page size, compression, caching, blocking scripts and image setup, so you can find causes even without lab data.
How to use it
- Open the Core Web Vitals Checker.
- Enter the page URL and choose mobile.
- Click Check Core Web Vitals.
- Focus on the metric marked worst first.
How to improve LCP
- Compress and resize the main image with the Image Size Optimizer.
- Do not lazy load the hero image. Lazy load only images further down.
- Improve server response with caching and a CDN.
- Reduce render blocking CSS and JavaScript.
How to fix CLS
- Always set width and height on images and videos.
- Reserve space for ads and embeds so they do not push content down.
- Avoid inserting banners above existing content after the page loads.
- Use font display swap carefully and preload key fonts.
How to improve interaction speed
- Remove heavy scripts you do not need.
- Defer third party widgets like chat, popups and social feeds.
- Break long JavaScript tasks into smaller pieces.
- Use fewer page builder animations.
Lab data versus field data
Lab data is a controlled test of one page load. Field data comes from real Chrome users over the past month. Google ranks using field data, but lab tests help you find and fix problems quickly. Small sites often do not have enough visitors for field data, so lab checks are the best guide.
A real example
A news site had a CLS problem. Readers complained the article jumped down just as they started reading. The cause was an ad slot without reserved space and images without dimensions. After setting fixed heights for ad containers and adding width and height to images, the layout stopped moving. Readers stayed longer and the page experience report in Search Console improved over the following weeks.
Common mistakes to avoid
A frequent mistake is fixing only the homepage. Google looks at groups of similar pages, so your product, category and blog templates matter just as much. Another mistake is lazy loading the main hero image. That image is usually the LCP element, so it should load right away with a high priority. Some owners also add cookie banners and chat widgets that push content down after the page appears, which hurts CLS. Reserve space for these elements or show them as overlays. Finally, remember that field data updates over about 28 days, so give your fixes time before you judge the result.
Frequently asked questions
Do Core Web Vitals strongly affect rankings
They are one signal among many. Great content still matters most, but good vitals help in close competition.
Why is there no field data for my site
Google only reports field data when enough real Chrome users visit the page.
Which metric should I fix first
Start with LCP on mobile, because slow loading affects every visitor.
Check your page now with the free Core Web Vitals Checker.