Performance and UX

CLS

Also known as: Cumulative Layout Shift

A measure of unexpected movement of visible page layout elements.

A practical example

A button moves when an image loads without reserved dimensions.

What should I know?

Not every layout change following a deliberate user action is a CLS problem.

Performance and UX in practice

Assess real users' experiences on their devices. Lab tests help identify causes, while user data shows the scale of a problem. A good website also makes information easy to find and tasks easy to complete.

Related Semly features

See where this concept applies when working with Semly.

Google Search ConsoleConnect search data to Semly. Analyze queries and page performance when planning next steps.AI analyticsCompare visibility, position, sentiment, and brand share in AI answers.

Related terms

Core Web VitalsUser experience metrics covering main content loading, interaction response, and layout stability.UXThe overall experience and difficulties of using a product or service.Image optimizationChoosing image dimensions, compression, format, and loading behavior for their use.

Documentation and further reading

Definition prepared by Semly. Standards and behavior are described by their creators:

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