Level A · WCAG 2.0
2.3.1 Three Flashes or Below Threshold
Nothing flashes more than three times per second.
Partly automated Some failures are detectable, others need judgement.
How it fails in practice
A celebratory confetti animation at checkout with rapid high-contrast strobing. This criterion exists because the failure can trigger a seizure.
How to fix it
Keep flashes under three per second, or remove the effect. Treat it as a safety requirement, not a style question.
At a glance
- Level
- Level A — the minimum. Failing one of these usually makes something impossible rather than merely hard.
- Principle
- Operable
- Guideline
- 2.3 Seizures
- Added in
- WCAG 2.0
- EN 301 549
- 9.2.3.1
- Automated check
- Partly automated
Partly automated
How far an automated check gets
A tool finds some failures here and cannot see the rest. A clean automated result means the checks that exist found nothing — not that the criterion is met. This is the gap that makes a green scan look like an accessible site, and it is where the keyboard agent, the agents still in development and a human reviewer do the remaining work.
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