WCAG Guideline 2.3.1: Three Flashes or Below Threshold Explained
Estimated read time: 6–7 minutes
Guideline 2: Operable
The Operable principle ensures that all users can interact with and control web content, regardless of their abilities. This includes protecting users from content that could cause physical harm, such as seizures.
Guideline 2.3: Seizures and Physical Reactions
Guideline 2.3 focuses on preventing content that could trigger seizures or other physical reactions, especially from flashing or strobing effects.
What Is Guideline 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."
Guideline 2.3.1 Three Flashes or Below Threshold is a Level A requirement in the Web Content Accessibility Guidelines (WCAG) .
- Content must not flash more than three times per second, unless it is below the defined thresholds for general and red flashes.
- Applies to videos, animations, banners, and any visual content.
- Protects users with photosensitive epilepsy and similar conditions.
This ensures your content is safe for users with photosensitive epilepsy and meets accessibility requirements.
For more, see BOIA: WCAG 2.3.1 Three Flashes or Below Threshold .
Why Does It Matter?
- Inclusivity: Flashing content can trigger seizures in people with photosensitive epilepsy.
- Legal Compliance: Three Flashes or Below Threshold is a Level A requirement in WCAG 2.1 and 2.2.
- Usability: Prevents discomfort and health risks for all users.
For more, see W3C’s guidance on flashing content .
What Needs to Avoid Flashing?
- Videos and animations
- Games and interactive content
- Any feature with flashing or strobing effects
All must avoid more than three flashes per second, or stay below the defined thresholds.
How to Avoid Flashing Content
- Avoid content that flashes more than three times per second
- Use safe animation techniques
- Test with users who are sensitive to flashing
- Document animation policies
For more, see the W3C's Three Flashes Techniques .
Common Mistakes to Avoid
- Content that flashes more than three times per second
- No warning about flashing content
- Not documenting animation policies
- Not testing with users who are sensitive to flashing
Differences Between A, AA, and AAA for Guideline 2.3.1 in WCAG 2.2
- Level A: Requires content does not flash more than three times per second or is below the threshold. This is the core requirement for 2.3.1 and is mandatory for basic accessibility.
- Level AA: For Guideline 2.3.1, there are no additional requirements beyond Level A in WCAG 2.2. Meeting Level A for this guideline also satisfies Level AA.
- Level AAA: For Guideline 2.3.1, there are no additional requirements beyond Level A in WCAG 2.2. Meeting Level A for this guideline also satisfies Level AAA.
For more, see the W3C’s official documentation for 2.3.1 Three Flashes or Below Threshold .
Quick Checklist
- No content flashes more than three times per second
- All animations are safe for users with epilepsy
- Animation policies are documented
- Tested with users who are sensitive to flashing
Summary
Guideline 2.3.1 is essential for preventing seizures and supporting users with photosensitive epilepsy. By avoiding flashing content, you support users with disabilities, improve usability, and meet legal requirements. Test your site regularly and make safe animation a core part of your development process.