2.3.1 Three Flashes or Below Threshold
Web pages do not contain anything that flashes more than three times in any one-second period, or the flash is below the general flash and red flash thresholds.
Last reviewed: September 9, 2026
Understanding 2.3.1
Flashing content can trigger seizures in people with photosensitive epilepsy, a serious and potentially life-threatening risk. This criterion prohibits content that flashes more than three times in any one-second period unless the flashing area and contrast fall below the general flash and red flash thresholds defined in WCAG, protecting users from seizure-inducing content.
How to Meet It
Frequently Asked Questions
Does a single bright flash count, or does it need to repeat?
The threshold concerns repeated flashing: more than three flashes within any one-second window. A single isolated flash, or flashing at three or fewer times per second, does not violate this criterion regardless of brightness, since rapid repetition is what poses the seizure risk.
How do I actually test content against this criterion?
Use an automated tool such as the Photosensitive Epilepsy Analysis Tool (PEAT) to analyze video or animated content frame-by-frame for flash rate and affected area against the general and red flash thresholds. Manual frame-by-frame counting is impractical for anything beyond the simplest animations.
Related Success Criteria
Quick Facts
- Criterion2.3.1
- LevelA
- IntroducedWCAG 2.0
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