Core Web Vitals Checker
Check Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift for any public page. See what real Chrome visitors experience, run a Lighthouse lab test, and get a plain-words list of what to fix first.
- Real-user data from Google
- Mobile and desktop tests
- Likely causes found in your code
Want the full picture of speed and weight? Run the Website Performance Checker, or check how links and redirects add delay with the Redirect Checker.
What Core Web Vitals measure
Google uses three user-experience metrics. A page passes when all three are good for at least 75 percent of real visits.
LCP: loading
Largest Contentful Paint is how long the biggest image or block of text takes to appear. Good is 2.5 seconds or less, poor is over 4 seconds.
INP: responsiveness
Interaction to Next Paint is how quickly the page reacts when someone taps, clicks or types. Good is 200 milliseconds or less, poor is over 500.
CLS: visual stability
Cumulative Layout Shift is how much content jumps around while the page loads. Good is 0.1 or less, poor is over 0.25.
Core Web Vitals thresholds at a glance
These are Google's published boundaries. The tool rates every number against them.
| Metric | Good | Needs improvement | Poor |
|---|---|---|---|
| LCP | 2.5 s or less | 2.5 s to 4 s | Over 4 s |
| INP | 200 ms or less | 200 ms to 500 ms | Over 500 ms |
| CLS | 0.1 or less | 0.1 to 0.25 | Over 0.25 |
| FCP | 1.8 s or less | 1.8 s to 3 s | Over 3 s |
| TTFB | 0.8 s or less | 0.8 s to 1.8 s | Over 1.8 s |
LCP, INP and CLS are the three Core Web Vitals. FCP and TTFB are supporting metrics that help explain a slow LCP.
How to check Core Web Vitals
Four steps from a URL to a fix list.
Enter a URL
Paste a public page and choose mobile or desktop. Google indexes mobile first, so start there.
Read the assessment
See whether the page passes, and switch between this page and the whole site if Google has both.
Check the lab test
Use the Lighthouse score and the opportunities list to find what slows the page down.
Fix and re-test
Work from the biggest time saving down. Field data takes up to 28 days to reflect changes, the lab test updates at once.
Field data and lab data answer different questions
The two kinds of numbers can disagree, and both are useful.
Field data: what visitors feel
Collected from real Chrome users over 28 days. It is what Google uses for ranking. It needs enough traffic, so small pages often have none.
Lab data: what to fix
One simulated load on a mid-range phone with a throttled network. It is repeatable and shows causes, but it is not what real visitors get.
What Core Web Vitals are and why they matter for SEO
Core Web Vitals are three measurements Google uses to describe how a page feels to a real visitor. Largest Contentful Paint (LCP) is how quickly the main content appears. Interaction to Next Paint (INP) is how quickly the page responds to taps, clicks and key presses. Cumulative Layout Shift (CLS) is how much the layout jumps while it loads. A page is rated good when LCP is 2.5 seconds or less, INP is 200 milliseconds or less and CLS is 0.1 or less, measured at the 75th percentile of visits and split by mobile and desktop. INP replaced First Input Delay in March 2024.
A Core Web Vitals checker shows you those numbers for a URL. The ones to read first are field data: measurements from real Chrome users, collected over a rolling 28 days. Lab data is a single simulated load. It is repeatable and good for finding causes, but it is not what your visitors get. Lab tools also cannot measure INP directly, because a test run has no real user input, so they use a proxy metric instead. That is why a page can score well in a lab test and still fail in the field.
Do Core Web Vitals affect rankings? Google says its ranking systems use them, and also that there is no single page experience signal and that good scores do not guarantee a top position. Treat them as one input among many, never as a substitute for relevant content. They matter on their own terms too: slow, jumpy pages lose visitors before the content has a chance to work. The Core Web Vitals guide on web.dev explains each metric in more depth.
When to check your Core Web Vitals
Check at least once per page template, and again whenever something that affects speed or layout changes.
After a redesign or theme change
A new theme, page builder or font setup can shift all three metrics at once. Test the home page, a product or article page and a category page, since each template behaves differently.
Before and after a speed project
Record the field numbers before developers start. The lab test reflects a fix at once, while real-user data needs up to 28 days to catch up, so keep the baseline for comparison.
When mobile feels worse than desktop
Switch between mobile and desktop results. Slower phones and networks often fail LCP or INP on pages that pass easily on a laptop.
For a client or management report
Real-user numbers from Chrome are easier to defend than one Lighthouse score. Pair them with the Core Web Vitals report in Search Console to show which page groups need work.
During a technical SEO audit
Find the template that fails and the metric that fails it. The list of likely causes points a developer to the first thing to try, such as an image, a script or a missing size.
To benchmark a competitor
Enter a competitor's page to see whether Google has real-user data for it. Where it does, you can compare how the two sites feel on the same device type.
Core Web Vitals mistakes and how to fix them
Most wasted effort comes from measuring the wrong thing or fixing the wrong page.
Trusting the lab score alone
What goes wrong: A green Lighthouse score does not mean visitors have a good experience. Lab data is one simulated load on one device profile, so it can pass while real visitors on slower phones fail.
The fix: Read the field data first and use the lab test to find causes. If the page has no field data yet, treat the lab score as a guide, not a verdict.
Expecting a fix to show up at once
What goes wrong: You deploy a fix, re-run the check and the field numbers look unchanged, so you assume it failed. Field data is a rolling 28-day window.
The fix: Confirm the fix in the lab test straight away, then wait for the window to roll over. Expect up to four weeks before the field numbers and Search Console fully reflect it.
Fixing one page instead of the template
What goes wrong: Optimising only the home page leaves every product, article or category page on the same slow template. Search Console groups similar URLs for this reason.
The fix: Find which template fails and fix it once. A change to a shared header, image component or script usually improves hundreds of pages together.
Lazy-loading the main image
What goes wrong: A theme or plugin adds lazy loading to every image, including the hero image that is the LCP element. That adds delay before the largest element even starts to load.
The fix: Never lazy-load the likely LCP image, and give it a high fetch priority. Keep lazy loading for images lower down the page.
Images and embeds without reserved space
What goes wrong: Images, ads and embeds with no width and height push the text down when they appear, which raises CLS. Web fonts that swap in late can also move lines of text.
The fix: Set width and height attributes (or a CSS aspect ratio), reserve space for ads and embeds with a minimum height, and choose a fallback font close in size to your web font.
Heavy scripts hurting responsiveness
What goes wrong: Tag managers, chat widgets and large JavaScript bundles keep the main thread busy, so taps wait before the page reacts. This is the usual cause of a poor INP.
The fix: Remove tags you no longer use, load non-essential scripts late, and ask developers to break long tasks into smaller ones so the browser can answer input between them.
Core Web Vitals terms explained
- LCP (Largest Contentful Paint)
- The time until the largest image, video poster or block of text in the viewport is drawn. Good is 2.5 seconds or less, and poor is over 4 seconds.
- INP (Interaction to Next Paint)
- How long the page takes to show a visual response after a click, tap or key press, across the whole visit. Good is 200 milliseconds or less, and poor is over 500.
- CLS (Cumulative Layout Shift)
- A score for unexpected movement of visible content during loading. It is a unitless number, not a time. Good is 0.1 or less, and poor is over 0.25.
- 75th percentile
- The value that 75 percent of visits meet or beat. A page passes a metric when this value is in the good range, so a slow minority of visits can still fail it.
- Field data
- Measurements collected from real users on their own devices and networks. It shows what visitors experience, but it needs enough traffic and reflects the past 28 days.
- Lab data
- Results from a controlled test, such as one Lighthouse run. It is repeatable and good for debugging, but it is a simulation and can differ from real-user experience.
- CrUX (Chrome UX Report)
- Google's public dataset of real Chrome user experience data. It supplies the field numbers in this tool, and it only covers pages and sites with enough visits.
- TTFB (Time to First Byte)
- How long the server takes to start answering. It is not a Core Web Vital, but a slow response eats into the time available for a good LCP.
Related tools, guides and services
Core Web Vitals tell you that a page is slow or unstable. These help you find why and fix it.
Website Performance Checker
See server response, page weight, render-blocking files and caching, the causes behind a slow LCP.
ToolImage SEO Checker
Find oversized images, missing dimensions and lazy-loading mistakes that hurt LCP and CLS.
GuideSEO audit errors that matter
See where Core Web Vitals sit among the issues a technical audit should prioritise.
GuideSEO for Nepali ecommerce
A practical look at speed and Core Web Vitals on mobile for online stores in Nepal.
ServiceTechnical SEO service
Get Core Web Vitals, crawling and rendering problems diagnosed and fixed by a specialist.
CourseAdvanced SEO course
Learn how to measure and improve Core Web Vitals as part of technical SEO training.
Built by
Madhav Kushwaha
SEO, AEO, GEO & Digital Marketing Consultant in Kathmandu, Nepal, and trainer at ODcrU Academy and TechAxis Institute. Core Web Vitals are a ranking signal, but the report most people see is a single Lighthouse score. I built this checker to put the real-user numbers first, because those are what Google measures, and to explain each failing metric in words a client can act on.
Core Web Vitals Checker: Frequently Asked Questions
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