What is measured
The audit uses the unitless CLS value; up to 0.1 is the good laboratory threshold.
Performance and mobile experience
Cumulative Layout Shift (CLS)
This check assesses unexpected movement of content that has already appeared during loading.
Pass criterion
Text, buttons and forms do not jump after images, fonts, banners or asynchronous blocks appear.
What to fix
Declare media dimensions, reserve dynamic space and avoid inserting content above an already rendered interface.
Automation limit
A single lab run may not reproduce rare banners or personalised blocks.
Reference