Core Web Vitals Checker
Analyze your page performance with Google's official PageSpeed Insights data.
What This Tool Does
The Core Web Vitals and PageSpeed Checker runs a Google Lighthouse audit on any URL and returns key performance metrics including Largest Contentful Paint (LCP), Interaction to Next Paint (INP), Cumulative Layout Shift (CLS), First Contentful Paint (FCP), and the overall performance score. Results are powered by the Google PageSpeed Insights API.
Inputs
- URL: Enter the full URL of the page you want to test.
- Device: Choose between mobile and desktop analysis.
How It Works
The tool sends your URL to the Google PageSpeed Insights API, which runs a Lighthouse audit and returns both lab metrics and Chrome User Experience Report (CrUX) field data when available. Lab data comes from a simulated page load, while field data reflects real user experiences collected over 28 days.
Understanding the Results
- Performance score (0-100): An overall score based on weighted lab metrics. 90 or above is good, 50-89 needs improvement, below 50 is poor.
- LCP: Time until the largest content element renders. Target: under 2.5 seconds.
- INP: Responsiveness to user interactions. Target: under 200 milliseconds.
- CLS: Visual stability during page load. Target: under 0.1.
- FCP: Time until the first content element renders. Target: under 1.8 seconds.
Contacting Lighthouse... (This takes 10-20 seconds)
Results Breakdown
ANALYSISOptimization Opportunities
| Opportunity | Est. Savings |
|---|---|
| Run analysis to see data | |
Step-by-Step Example
- Enter a URL such as
https://example.comin the URL field. - Select Mobile or Desktop as the test device.
- Click Analyze to start the Lighthouse audit.
- Review the performance score. If below 90, look at individual metrics to identify issues.
- Check LCP. If above 2.5s, optimize images, use a CDN, or reduce server response time.
- Check CLS. If above 0.1, add dimensions to images and avoid injecting content above the fold.
Use Cases
- Benchmarking page speed before and after performance optimizations.
- Monitoring Core Web Vitals across key landing pages.
- Comparing mobile vs desktop performance for responsive design audits.
- Diagnosing slow pages that may be affecting search rankings.
- Generating performance data for client reports and stakeholder presentations.
Limitations and Notes
- Lab data may differ from field data because it uses a simulated environment.
- CrUX field data is only available for URLs with sufficient Chrome traffic.
- Results can vary between runs due to server conditions and network variability.
- The tool uses the Google PageSpeed Insights API, which has rate limits.
- INP field data requires real user interactions and may not be available for low-traffic pages.
Frequently Asked Questions
What are Core Web Vitals?
Core Web Vitals are a set of three metrics defined by Google that measure user experience: Largest Contentful Paint (LCP) measures loading speed, Interaction to Next Paint (INP) measures interactivity responsiveness, and Cumulative Layout Shift (CLS) measures visual stability.
What is a good LCP score?
A good LCP score is 2.5 seconds or less. LCP between 2.5 and 4 seconds needs improvement, and above 4 seconds is poor. LCP measures how long it takes for the largest visible element to render on screen.
What is INP and how does it replace FID?
Interaction to Next Paint (INP) replaced First Input Delay (FID) as a Core Web Vital in March 2024. INP measures the responsiveness of all interactions throughout the page lifecycle, not just the first one. A good INP is 200 milliseconds or less.
Do Core Web Vitals affect search rankings?
Yes. Core Web Vitals are part of Google's page experience ranking signals. Pages with good CWV scores may receive a small ranking boost, especially in competitive queries where content quality is similar across results.
What is the difference between lab data and field data?
Lab data comes from controlled Lighthouse tests and is useful for debugging. Field data (CrUX) comes from real Chrome users over a 28-day period and reflects actual user experience. Google uses field data for ranking decisions.
How can I improve my CLS score?
Set explicit width and height attributes on images and videos, avoid inserting content above existing content, use CSS contain property for dynamic elements, and preload web fonts to prevent layout shifts during font loading.
Sources and References
- web.dev - Core Web Vitals: web.dev
- Google Search Central - Page Experience: developers.google.com
- web.dev - Largest Contentful Paint: web.dev
- web.dev - Interaction to Next Paint: web.dev
- web.dev - Cumulative Layout Shift: web.dev
- Chrome UX Report: developer.chrome.com