Cumulative Layout Shift (CLS) measures unexpected movement of visible page elements as a page loads — for example, text jumping down because an image above it loaded late without a reserved space. A lower CLS score, measurable with Google PageSpeed Insights (opens in new tab), means a more visually stable page.
Why This Specific Annoyance Got Its Own Metric
Almost everyone has tapped a button on a phone only to have the page jump right as the tap registered, hitting an ad or the wrong link entirely. CLS exists specifically because that experience is common enough, and frustrating enough, that Google decided to measure and reward pages that avoid it, treating stability as its own dimension separate from raw loading speed.
Web fonts loading in late and changing the size of visible text is another common, less obvious cause of layout shift that’s easy to overlook during testing.
Ads and embedded widgets injected after the initial page load are frequent offenders too, since they insert new content into a layout that has already settled.
People also ask
How do I fix a bad CLS score?
Reserve exact width and height space for images and embeds before they load, and avoid inserting new content above existing content after the initial page load.
See also
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