Technical SEO · Intermediate

Cumulative Layout Shift (CLS)

Cumulative Layout Shift (CLS) measures how much a page's content unexpectedly moves while it loads, like a button jumping as an image appears. It's the Core Web Vitals metric for visual stability; 0.1 or less is good.

By Thryv StudioUpdated

Level
Intermediate
Also called
CLS
Good
0.1 or less
Poor
More than 0.25

What is CLS?

CLS scores unexpected layout shifts: how much visible content moves and how far. Shifts right after a user's action don't count; shifts that happen on their own do.

Common causes

  • Images and videos without width and height.
  • Ads, embeds and banners inserted without reserved space.
  • Web fonts that swap in with different sizes.
  • Content injected above existing content.

How to fix it

  1. Set width and height (or aspect-ratio) on images and videos.
  2. Reserve space for ads, embeds and late-loading elements.
  3. Use font-display settings and similar fallback fonts.
  4. Add new content below what the visitor is reading.

Frequently asked questions

Does CLS include shifts after the page loads?

Yes, across the visit, grouped into windows; the worst window is reported.

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