2.3.1 Three Flashes or Below Threshold

MCS Accessibility Team

MCS Accessibility Team
Last Updated July 23, 2020

The following directions are part of a full step-by-step guide to making a HubSpot website WCAG 2.1 AA compliant. These recommendations are intended for websites managed on the HubSpot CMS but can be adapted for other content management systems.

Principle: Operable
User interface components and navigation must be operable.
Guideline: Seizures and Physical Reactions
Do not design content in a way that is known to cause seizures or physical reactions.

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.

Note 1: Since any content that does not meet this success criterion can interfere with a user's ability to use the whole page, all content on the Web page (whether it is used to meet other success criteria or not) must meet this success criterion. See Conformance Requirement 5: Non-Interference.

View Official WCAG 2.1 Compliance Techniques

Understanding 2.3.1 Three Flashes or Below Threshold

Criterion 2.3.1 states that elements on a web page must not flash more than three times in a single second, or fall below the thresholds for general and red flashes. Its intention is to provide an accessible experience for those who may are photosensitive and may experience seizures.

If you have any videos or animation present on your site that you feel may not meet the criteria, you can run them through the Trace Center's Photosensitive Epilepsy Analysis Tool (PEAT) before uploading to your site.


  • Anything embedded on a web page does not apply to these guidelines. 
  • If the flashing content is below a specific size (that's dependent on viewport) it passes the criterion regardless of the flash threshold. 

For more information, please visit the official W3C article: Understanding 2.3.1 Three Flashes or Below Threshold


Let us know if we can help you address this specific WCAG Recommendation.