a11y/no-flash

Why

Flashing between light and dark more than three times a second can trigger seizures in people with photosensitive epilepsy. It is one of the few accessibility failures that can cause physical harm.

Fix

Keep alternating light and dark animations slower than three cycles per second, and avoid saturated red flashes. Check videos and game effects with a flash analysis tool before release, and wrap any strong effect in @media (prefers-reduced-motion: no-preference).

Examples

/* bad: a full-screen alert blinking eight times a second */
.alarm { animation: blink 125ms steps(2) infinite; }
/* good: a slow pulse, off when people ask for less motion */
@media (prefers-reduced-motion: no-preference) { .alarm { animation: pulse 2s ease-in-out 3; } }

Sources

• WCAG 2.2, Understanding SC 2.3.1 Three Flashes or Below Threshold

Read it in the terminal

npx github:dawidolko/frontend-skills explain a11y/no-flash