WCAG 2.3.1: Three Flashes or Below Threshold
WCAG 2.3.1 Three Flashes or Below Threshold is a level A success criterion from WCAG 2.0. Pages must not contain anything that flashes more than three times in one second, unless the flash is below the general flash thresholds.
Flashing can trigger seizures.
How to test
Watch carousels, ads and error animations. Nothing should strobe.
How to fix
Remove strobing animations and rapid colour flips.
Example that fails
A sale banner flashes red and white several times a second.
Example that passes the check
The banner is still, or it fades once.
Shopify
Delete theme CSS animations that toggle opacity or colour faster than three times a second.
WooCommerce
Remove strobe effects from sliders.
WordPress
Do not add flash animations in custom CSS.
Wix
Remove flashing strip animations.