Core Web Vitals Monitor
Analyze LCP, INP and CLS for any URL using Google PageSpeed API. Get performance score and improvement recommendations.
What are Core Web Vitals and why do they matter for SEO?
Core Web Vitals (CWV) are three metrics defined by Google to measure real user experience on a web page: loading speed, responsiveness and visual stability. Since May 2021 they are an official ranking factor within Google's Page Experience algorithm. A site with good CWV has an advantage over competitors with similar content but worse technical performance.
Google uses Core Web Vitals as a tiebreaker signal: if two pages have similar content, the one that delivers a better user experience will tend to rank higher.
The three Core Web Vitals metrics explained
LCP measures the time it takes for the largest visual element on the page (usually a hero image or main text block) to render. It is the metric most directly related to the user's perception of speed.
Bueno: ≤ 2.5 seconds — fast experience
Necesita mejora: 2.5s – 4.0s — improvable experience
Malo: > 4.0s — slow experience, negative SEO impact
How to improve:
Optimize and compress images (WebP/AVIF), use lazy loading only for images below the fold, implement a CDN, add preload for the LCP resource, and improve server TTFB.
INP measures the response time from when the user clicks, taps or presses a key to when the browser visually updates the screen. It replaced FID in March 2024. It particularly penalizes pages with heavy JavaScript that blocks the main thread.
Bueno: ≤ 200 ms — immediate response
Necesita mejora: 200ms – 500ms — acceptable but improvable response
Malo: > 500ms — slow response, frustrated users
How to improve:
Split JavaScript into smaller chunks (code splitting), remove unnecessary third-party scripts, use web workers for heavy tasks and prioritize hydration of interactive components.
CLS measures how much visible content shifts unexpectedly during loading. A high CLS causes accidental clicks and a poor user experience. The most common causes are images without defined dimensions, variable-size ads and web fonts that change the layout when they load.
Bueno: ≤ 0.1 — stable page
Necesita mejora: 0.1 – 0.25 — occasional shifts
Malo: > 0.25 — unstable page, very poor experience
How to improve:
Always define width and height attributes on images and videos, reserve space for ads and embeds, use font-display: optional or swap for web fonts, and avoid inserting elements above existing content.
Lab data vs. field data
There are two ways to measure Core Web Vitals: lab data (synthetic measurements under controlled conditions) and field data (real measurements from real users collected by Chrome). This tool uses lab data via Lighthouse through the Google PageSpeed Insights API.
Lab data (this tool)
Synthetic measurement run by Lighthouse on Google's servers. Reproducible, immediate and without the need for prior traffic. Ideal for detecting issues and measuring the impact of technical changes before publishing.
Field data (CrUX)
Real data collected from Chrome users over the past 28 days. These are the values Google uses directly as a ranking signal. Available in Google Search Console and PageSpeed Insights when there is enough traffic.