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Layout shift (CLS)

performance.cwv_cls_poor
Priority
Medium
Severity
Critical

What we look for

In Google's PageSpeed Insights test (one lab load of each page), these pages scored more than 0.25 for CLS (Cumulative Layout Shift), a measure of how much the content moves while the page loads.

Why it matters

CLS is one of Google's Core Web Vitals (page experience scores), and this is rated Poor. Moving content makes visitors lose their place or tap the wrong thing.

How to fix

Give images, videos, ads and embeds a fixed width and height or reserved space in the page template, and avoid adding banners or content above what has already loaded.

What it cannot know

This is one lab load per page. Shifts caused by scrolling or tapping, which real visitors see, are not included.

Where you’ll see it

The id is stable, and every surface uses it, so it’s the thing to search for or hand to an agent.

Terminal
When it is one of the five findings under Fix first, raptor crawl prints the id under it.
Check: performance.cwv_cls_poor
crawl.json and the CSV
The crawl JSON names the finding by this id, and so do the CSV and raptor_query.
"check_id": "performance.cwv_cls_poor"
The HTML report
This link opens the finding in the report, and each finding shows its id.
crawl.html#finding=performance.cwv_cls_poor
MCP
raptor_findings with this check_id returns the finding in full, with a fix brief ready to paste into a task. If it didn’t fire, it says why.
raptor_findings {
  "job_id": "...",
  "check_id": "performance.cwv_cls_poor"
}