Performance
Free CLS Checker
Cumulative Layout Shift (CLS) measures how much the page jumps while loading. Check this page when CLS data is available.
Focus: CLS
Guide
What is CLS?
CLS scores unexpected movement of visible content — ads, images, or fonts without reserved space often cause it. 0.1 or less is typically good.
Why it matters
Layout shifts make buttons and links move under the user's finger — frustrating on mobile.
Common problems
- Images/videos without width/height
- Ads or embeds injecting space late
- Web fonts swapping late without fallback
How to fix them
Reserve space with explicit dimensions, use font-display strategies, and avoid inserting banners above existing content.
Example
Example: CLS 0.28 → set image dimensions and reserve ad slots.
FAQ
What is a good CLS?
0.1 or less is typically good; above 0.25 is poor.
Is CLS always available?
Only when measured — otherwise the report shows Not available.
Is it free?
Yes.