Core Web Vitals Scorer
Score Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift against the official thresholds, with the pass rule explained and the weakest metric identified.
Last reviewed by the Radiatus Cloud team
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The thresholds and the rule that combines them
Largest Contentful Paint should be at or under 2.5 seconds, Interaction to Next Paint at or under 200 milliseconds, and Cumulative Layout Shift at or under 0.1. A page passes the assessment only when all three are within the good band, so a single failing metric fails the whole set. The values that matter are the 75th percentile of real visits, not a lab measurement, which means a quarter of your visitors can be slower than the threshold and the page still passes.
Field data and lab data measure different things
A lab test runs on one device and one connection, with no extensions, no cold cache and no real user behaviour. Field data comes from actual visits across the full range of devices and networks your audience uses, and it is what the assessment is based on. Lab tools are for diagnosis, since they tell you which resource is slow, and field data is for measurement. A page that scores well in a lab test and fails in the field usually has a real audience on slower devices than the test machine.
INP replaced First Input Delay for a reason
First Input Delay measured only the delay before the first interaction was processed, which meant a page could score perfectly while every subsequent interaction was slow. Interaction to Next Paint measures the full duration from interaction to the next visual update, across all interactions during the visit, reporting close to the worst one. It is a considerably harder metric to pass and it reflects what a user actually experiences.
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Frequently Asked Questions
Does a page pass if only one metric fails?
No. All three must be within the good band for the assessment to pass. A single failing metric fails the set, which is why the weakest metric is worth identifying before spending effort elsewhere.
What does the 75th percentile mean?
That three quarters of visits were at or better than that value. It is measured across real visits rather than a lab test, so a quarter of your users can be slower than the threshold while the page still passes.
Why did INP replace First Input Delay?
Because First Input Delay measured only the delay before the first interaction was processed. A page could score perfectly while every later interaction was slow. INP measures the full time from interaction to the next visual update, across all interactions, and reports close to the worst.
Why does my lab score differ from field data?
Because a lab test uses one device, one connection, a cold cache and no extensions, while field data covers the full range of real devices and networks. Use lab tools to diagnose which resource is slow and field data to know whether you are actually passing.
Do Core Web Vitals affect rankings?
They are a ranking signal and a small one relative to relevance and links. The stronger argument for fixing them is that the same problems cause abandoned visits and lost conversions, which are measurable regardless of any ranking effect.
Privacy & Security
Everything runs in your browser; nothing is uploaded.
How to Use
Enter your LCP, INP and CLS values to see whether the page passes and which metric to fix first.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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