Free CLS Tester & Analyzer
Test and analyze your Cumulative Layout Shift (CLS) score. Measures this page's layout shifts in the browser or analyzes a score from PageSpeed Insights.
CLS Score Analyzer
From PageSpeed Insights or Chrome DevTools
CLS Thresholds
Good
< 0.1
Needs Improvement
0.1 – 0.25
Poor
> 0.25
Common CLS Causes & Fixes
Images without dimensions
Always set width and height attributes on <img> tags. Use aspect-ratio CSS.
Ads without reserved space
Reserve space for ad slots with min-height so content doesn't shift when ads load.
Dynamically injected content
Avoid inserting content above existing content. Use transform animations instead.
Web fonts (FOUT/FOIT)
Use font-display: optional or swap. Preload critical fonts. Use size-adjust.
iframes without dimensions
Set explicit width and height on iframes. Use aspect-ratio for responsive iframes.
CSS animations that trigger layout
Use transform and opacity for animations instead of properties that trigger layout.
CLS measures visual stability — how much page content unexpectedly shifts while loading. It's a Core Web Vital that affects Google search rankings. Measure with PageSpeed Insights.
Frequently Asked Questions
What is CLS?
Cumulative Layout Shift measures how much page content unexpectedly shifts during loading. Lower is better.
What is a good CLS score?
Under 0.1 is Good. 0.1–0.25 needs improvement. Over 0.25 is Poor.
Is it free?
Yes, completely free.
Is my data safe with this tool?
Absolutely. The CLS Tester & Analyzer processes everything client-side in your browser. No data is uploaded to or stored on any server. Your content remains private on your device at all times.
Does the CLS Tester & Analyzer work on mobile devices?
Yes, the CLS Tester & Analyzer is fully responsive and works on smartphones and tablets. You can use it on any device with a modern web browser -- no app download required.
Do I need to create an account to use this tool?
No account or registration is needed. Simply open the CLS Tester & Analyzer in your browser and start using it immediately. There are no sign-up walls or usage restrictions.
Does this tool follow Google's latest guidelines?
Yes, the CLS Tester & Analyzer is built following current Google Search guidelines and best practices. We regularly update the tool to reflect changes in search engine requirements.
How do I use the CLS Tester & Analyzer?
Simply enter your input in the provided field, adjust any settings to your preference, and the tool will process it instantly. You can then copy the result to your clipboard or download it.
Which browsers are supported?
The CLS Tester & Analyzer works in all modern browsers including Chrome, Firefox, Safari, Edge, and Opera. For the best experience, use the latest version of your preferred browser.
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About Free CLS Tester & Analyzer
Free CLS Tester & Analyzer is a free, browser-based tool in our SEO Tools collection. Everything runs locally on your device — no uploads, no sign-up, and your data stays private.