What is CLS (Cumulative Layout Shift)?

CLS (Cumulative Layout Shift) is a Core Web Vitals metric that measures how much and how unexpectedly elements on a page shift during its loading. It shows the visual stability of the interface.

If images, text, buttons, or banners suddenly "jump" during loading, that's bad CLS. A user can:

• miss a button,
• lose their place in a text they were reading,
• accidentally click the wrong thing.

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#What CLS reflects

CLS isn't about speed. It's a metric about display quality and usability. It captures unexpected shifts of elements that happen without any user action.

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#Google's thresholds

• Good: ≤ 0.1
• Needs improvement: 0.11-0.25
• Poor: > 0.25

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#Typical causes of bad CLS

• images without specified width/height,
• ad banners that load later and push content down,
• dynamic elements (banners, pop-ups) without pre-reserved space,
• fonts that change text size after loading.

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#Why it matters

CLS affects the sense of control and comfort. Even a fast page feels "broken" and annoying if the interface jumps around. Which means a higher bounce rate, and lower engagement and conversion.

Conclusion: CLS is about a stable, predictable interface. The fewer visual jumps, the better the user experience and the SEO signals.