Three Flashes or Below Threshold (2.3.1)

Pages must not contain anything that flashes more than three times per second, unless the flash is below general flash and red flash thresholds.

WCAG Reference

Applies to: WCAG 2.0, WCAG 2.1, WCAG 2.2 Introduced in: WCAG 2.0 | Level: A | Read the official specification →

What this rule checks

The scanner flags content that produces rapid flashing (more than three flashes per second) in a large enough area to exceed safety thresholds.

Why it matters

Rapid flashing can trigger seizures in people with photosensitive epilepsy. This is a critical safety requirement, not just a usability concern.

Common failure patterns

• animated GIFs or videos with rapid light-to-dark transitions
• strobe effects in promotional content or loading animations
• rapid color cycling in game-like or interactive elements
• auto-playing video ads with flashing transitions

Remediation guidance

• limit flashing to three or fewer per second in any region of the page
• use the Photosensitive Epilepsy Analysis Tool (PEAT) to test video and animation content
• provide a warning before content that contains known flashing and allow the user to skip it
• respect prefers-reduced-motion to suppress flashing animations

Related docs

• Web Rule Repository
• Accessibility Issue Remediation Guide