Medium impactPerformance
High Cumulative Layout Shift (CLS)
Pages that jump around as they load fail CLS. Here's how to lock the layout in place.
What it means
Visible elements shift position unexpectedly as the page loads, scoring above 0.1 on Cumulative Layout Shift.
Why it matters
CLS is a Core Web Vitals metric. It's also one of the most annoying UX issues — users tap the wrong thing because the page jumped.
How to fix it
- Set explicit width and height on all <img>, <video>, and <iframe> elements.
- Reserve space for ads and embeds with min-height containers.
- Use font-display: optional or preload fonts to avoid swap shifts.
- Don't insert content above existing content (banners, alerts).
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Frequently asked questions
What's the CLS target?
Under 0.1 to pass. Under 0.05 is comfortably good.