Core Web Vitals Checker — LCP, CLS & INP Score Tester
Test LCP, CLS, and INP scores for mobile and desktop with Google PageSpeed Insights data. Fix Core Web Vitals issues fast. Free tool for any website owner.
What is a Core Web Vitals Checker?
The Core Web Vitals Checker retrieves detailed LCP, CLS, and INP data for any URL from the Google PageSpeed Insights API, displaying both field data — real-user measurements from the Chrome User Experience Report — and lab data from a controlled simulation. Each metric is shown against Google's official Good, Needs Improvement, and Poor thresholds, with separate desktop and mobile views and distribution charts for field data.
When Should You Use Core Web Vitals Checker?
Use this when you need to understand the specific Core Web Vitals signals that influence Google's Page Experience ranking factor. Unlike a general performance score, this tool focuses on the three metrics Google uses for ranking: Largest Contentful Paint, Cumulative Layout Shift, and Interaction to Next Paint. Use it when diagnosing a page that is failing the Core Web Vitals assessment in Google Search Console, or when you want to understand exactly which metric is the bottleneck.
How to Read Core Web Vitals Checker Results
Field data reflects actual user experience and is what Google uses for ranking decisions — it may differ from lab data because it captures real device and network conditions. A page passes the Core Web Vitals assessment only when all three metrics are in the Good range in field data for both mobile and desktop. One failing metric fails the whole assessment regardless of how good the others are.
What Should You Know Before Using Core Web Vitals Checker?
LCP above 2.5 seconds is most commonly caused by a large hero image, render-blocking resources, or slow server response time. CLS above 0.1 is typically caused by images without defined dimensions, late-loading ads, or dynamically injected content that shifts layout after initial paint. INP above 200ms points to slow JavaScript interaction handling. Always fix the metric with the worst field data first — that is what Google is measuring and what affects your ranking.
Frequently Asked Questions
What are Core Web Vitals?
Core Web Vitals are three Google metrics that measure real-world page experience: Largest Contentful Paint (LCP) measures loading speed, Cumulative Layout Shift (CLS) measures visual stability, and Interaction to Next Paint (INP) measures responsiveness. Google uses these as ranking factors in its Page Experience system.
What are the Core Web Vitals thresholds for Good?
Google's Good thresholds are: LCP under 2.5 seconds, CLS under 0.1, and INP under 200 milliseconds. Needs Improvement ranges are LCP 2.5–4s, CLS 0.1–0.25, and INP 200–500ms. A page must meet all three Good thresholds in field data to pass the Core Web Vitals assessment in Google Search Console.
What causes a high LCP score?
LCP above 2.5 seconds is most commonly caused by unoptimised hero images (large file size or wrong format), render-blocking CSS and JavaScript that delays the page from painting, slow server response times (TTFB above 600ms), and resources loaded from slow third-party origins. Optimising the LCP image and eliminating render-blocking resources typically yields the largest gains.
What causes Cumulative Layout Shift?
CLS above 0.1 is typically caused by images and video elements without explicit width and height attributes, web fonts causing a flash of unstyled text that shifts content on load, dynamically injected ads or banners that push down existing content, and late-loading widgets that displace page elements after initial paint.
What is INP and how is it different from FID?
Interaction to Next Paint (INP) measures the time from any user interaction (click, tap, keyboard input) to when the browser next paints a response. It replaced First Input Delay (FID) as a Core Web Vital in March 2024 because INP measures all interactions throughout a page session, not just the first one, giving a more complete picture of responsiveness.
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