Free Core Web Vitals Measurement Tool

Measure LCP, CLS, INP and performance scores.
Diagnose page speed for both mobile and desktop.

What are Core Web Vitals?

Google's official page-experience metrics that score a page's load time, visual stability and responsiveness using three signals: LCP, CLS and INP.

Three metrics: LCP (loading), CLS (stability), INP (responsiveness)
Good thresholds: LCP ≤ 2.5s, CLS ≤ 0.1, INP ≤ 200ms
Source: Google PageSpeed Insights API
Ranking impact: Official ranking factor since June 2021

Best for: Developers and site owners who suspect their pages load or respond too slowly

What Are Core Web Vitals?

Three user experience metrics defined by Google. Included as a search ranking factor since 2021.

LCP (Largest Contentful Paint)

Time until the main content is visible. Under 2.5 seconds is "good". Image optimization and server response time are key.

CLS (Cumulative Layout Shift)

How much the layout shifts during loading. Under 0.1 is "good". Set image dimensions and reserve ad space.

INP (Interaction to Next Paint)

Response time to user interactions. Under 200ms is "good". Optimize heavy JavaScript and reduce main thread load.

Performance Score

Google Lighthouse-based 0-100 score. 90+ is "good". Evaluated separately for mobile and desktop.

Why Core Web Vitals Matter

Core Web Vitals are a Google search ranking factor. With equal content quality, sites with better Core Web Vitals scores rank higher, especially in mobile search.

Speed improvements directly impact conversions. Google's research shows that when page load increases from 1 to 3 seconds, bounce rate increases by 32%.

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FAQ

What are Core Web Vitals?▾

Three user experience metrics defined by Google (LCP, CLS, INP). Included as a search ranking factor since 2021, they evaluate page speed and interactivity.

What are the Core Web Vitals thresholds?▾

LCP under 2.5 seconds, CLS under 0.1, and INP under 200ms are considered "good". Performance score of 90+ is good.

Can you measure both mobile and desktop?▾

Yes. We use the Google PageSpeed Insights API to measure LCP, CLS, INP, and performance scores for both mobile and desktop.

What is the difference between INP and FID?▾

FID only measured the delay of the first interaction. INP measures responsiveness of all interactions on the page. Google deprecated FID in favor of INP in March 2024.

What are the main causes of slow LCP?▾

Hero image loading delays are the most common cause. Unoptimized images, slow server response, and render-blocking CSS/JS also contribute.

Does poor Core Web Vitals affect search rankings?▾

It's part of page experience signals, but content quality and relevance have greater impact. However, improved UX and lower bounce rates provide indirect SEO benefits.

Core Web Vitals: Pass Thresholds for All 3 Metrics

Core Web Vitals are the three metrics Google uses to evaluate page experience. INP officially replaced FID as the responsiveness metric in March 2024.

Pass / Needs Improvement / Poor Thresholds by Metric

Metric	Good	Needs Improvement	Poor
LCP (Largest Contentful Paint)	≤2.5秒	2.5–4.0 s	>4.0秒
INP (Interaction to Next Paint)	≤200ms	200–500 ms	>500ms
CLS (Cumulative Layout Shift)	≤0.1	0.1–0.25	>0.25

Key Improvement Tips by Metric

LCP

Image optimization (WebP, proper sizing)
Reduce server response time (improve TTFB)
Preload critical resources (rel=preload)

INP

Split heavy JavaScript (code splitting, lazy loading)
Reduce main thread load (break up long tasks)

CLS

Specify explicit width and height for images, videos, and ad slots
Control web font loading (font-display: swap)

An honest note: This tool performs lab measurements (a single per-URL measurement), while Google's official evaluation is based on real-user field data (CrUX). Lab values and field values may differ.