The page looks loaded, a visitor moves to click something, and everything jumps a moment before their tap lands — on the wrong thing. This is Cumulative Layout Shift, and it's both a conversion problem and a Google ranking signal.
Cumulative Layout Shift is one of Google's three Core Web Vitals — it scores how much visible content unexpectedly moves position after the page has started rendering. A low score means what a visitor sees stays where they expect it; a high score means elements are jumping around while they're trying to interact with the page.
If an <img> tag doesn't specify a width and height (or the CSS equivalent), the browser doesn't know how much space to reserve before the image file actually downloads. Everything below it renders first, then gets shoved down the moment the image loads in.
If custom fonts load after the initial text render, the browser first shows a fallback font, then swaps it once the real font arrives — and if the two fonts have different letter widths, every line of text reflows, shifting everything below it.
A cookie banner, a promo bar, or an ad that gets inserted above content that's already visible pushes everything down at that exact moment — often right when a visitor is mid-click.
Beyond the obvious — a visitor who taps the wrong button because it moved right as they clicked, and either bounces or converts on the wrong thing — CLS is also one of the signals Google uses directly in Core Web Vitals, which factors into ranking. It's one of the few issues that's genuinely bad for both conversion rate and SEO at the same time.
width/height attributes or aspect-ratio CSS to every image and embedfont-display: optional/swap with a closely-matched fallback so the swap doesn't reflow textLayout shift is measured automatically as part of every audit we run.
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