Reduce ad-related layout shift

  • Cumulative Layout Shift (CLS) quantifies the total visual instability caused by ad iframes shifting or inducing layout changes, using the Layout Instability API and layout shift scores.

  • This metric helps pinpoint areas for improvement and track progress rather than diagnosing specific issues.

  • Minimizing layout shift is crucial and involves pre-setting ad element sizes, though achieving perfection is challenging, especially with dynamic ads.

  • Refer to the GPT developer guide for best practices in minimizing layout shift for most scenarios.

Overview

Cumulative Layout Shift measures the total amount of user-visible layout shift using the Layout Instability API by summing the layout shift score for all layout shifts where the ad iframe shifted or caused the layout shift.

Recommendations

This metric is not indicative of a specific issue. It should be used to help identify areas for improvement and track that improvement over time.

To avoid layout shift, it's important to set sizes for ad elements before the ad tag loads. This can be difficult or impossible to do perfectly—especially for ad slots that accept dynamically sized ads—but there are best practices you can follow to minimize layout shift in most cases. For more information, see the guide to minimizing layout shift at the GPT developer site.

More information

Cumulative Layout Shift (CLS)

Optimize Cumulative Layout Shift