Core Web Vitals Checker
Instantly check your Core Web Vitals scores — LCP, CLS, FCP, TTFB, and Total Blocking Time — for mobile and desktop. Powered by Google PageSpeed Insights with actionable fix suggestions.
Powered by Google PageSpeed Insights. Takes 10–30 seconds.
How to Check Your Core Web Vitals
Enter any URL in the field above. Choose Mobile or Desktop — Google evaluates them independently and you should test both. Click Check Vitals and wait 10–30 seconds for the Google PageSpeed Insights API to return results.
Results show your three primary Core Web Vitals (LCP, CLS, FCP) as large cards with Good / Needs Improvement / Poor badges, plus additional metrics (TTFB, TBT, Speed Index) and a prioritised list of opportunities.
Core Web Vitals Thresholds at a Glance
| Metric | Good | Needs Improvement | Poor |
|---|---|---|---|
| LCP — Largest Contentful Paint | < 2.5s | 2.5s – 4.0s | > 4.0s |
| CLS — Cumulative Layout Shift | < 0.1 | 0.1 – 0.25 | > 0.25 |
| INP — Interaction to Next Paint | < 200ms | 200ms – 500ms | > 500ms |
| FCP — First Contentful Paint | < 1.8s | 1.8s – 3.0s | > 3.0s |
| TTFB — Time to First Byte | < 0.8s | 0.8s – 1.8s | > 1.8s |
Understanding Each Core Web Vital
LCP — Largest Contentful Paint
Measures when the largest above-the-fold element (usually a hero image or headline) fully renders. Slow LCP is usually caused by slow server response, render-blocking resources, slow resource load times, or client-side rendering delays.
CLS — Cumulative Layout Shift
Measures how much the visible page content unexpectedly shifts. Common causes: images without dimensions, dynamically injected content, web fonts causing a FOUT/FOIT, animations that trigger layout recalculation.
INP — Interaction to Next Paint
Replaced FID in March 2024. Measures responsiveness across all interactions during a page visit. High INP is caused by long JavaScript tasks on the main thread, excessive DOM size, or poorly optimised event handlers.
TTFB — Time to First Byte
The time from the request being sent to the first byte of the response arriving. A high TTFB indicates server-side issues: slow database queries, no edge caching, too far from the user, or inadequate server resources.
Lab Data vs. Field Data
This tool shows lab data (Lighthouse simulation) which is reproducible and great for development. Google Search Console and the CrUX report show field data (real-user measurements). Both matter — lab data helps you diagnose issues, while field data is what Google actually uses for the Page Experience ranking signal. Aim to pass both.
Frequently Asked Questions
What are Core Web Vitals?
Core Web Vitals are Google's user experience metrics that measure three critical aspects of page quality: LCP (Largest Contentful Paint) measures loading performance — how long it takes for the main content to appear; CLS (Cumulative Layout Shift) measures visual stability — how much the layout unexpectedly shifts while loading; and INP (Interaction to Next Paint), which replaced FID in March 2024, measures interactivity — how responsive the page is to user input. Together they give a holistic view of real-world user experience.
Do Core Web Vitals directly affect Google rankings?
Yes. Core Web Vitals became a confirmed ranking signal in June 2021 via Google's Page Experience update. Pages that meet the 'Good' threshold for all three metrics (LCP <2.5s, CLS <0.1, INP <200ms) may receive a ranking boost, while pages in the 'Poor' range can be deprioritised in competitive SERPs. The impact is most pronounced in queries where multiple pages have similar content quality — page experience becomes a tiebreaker.
What is a good LCP score?
Under 2.5 seconds is 'Good' and means your main content loads fast enough for a positive user experience. Between 2.5 and 4 seconds is 'Needs Improvement' — users may notice the delay. Over 4 seconds is 'Poor' and is likely hurting both user satisfaction and rankings. LCP is typically the hardest Core Web Vital to optimise because it depends on server response time, render-blocking resources, resource load time, and client-side rendering.
How do I fix a high CLS score?
The most effective fixes for high CLS are: (1) Reserve space for images and video by setting explicit width and height attributes — browsers can then allocate the correct space before the resource loads. (2) Avoid inserting content above existing content in response to user interaction; animate from off-screen instead. (3) Use CSS aspect-ratio boxes or padding-top hacks for responsive embeds. (4) Ensure web fonts don't cause a layout shift — use font-display: optional or font-display: swap with a closely matching fallback font. (5) Animate only transform and opacity properties, which do not trigger layout recalculation.
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