2.3.1 Three Flashes or Below Threshold (A)

Avoid any content which flashes more than 3 times a second.

What WCAG says:

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.

Check the official guidance for Understanding 2.3.1 Three Flashes or Below Threshold

What this means

A page must not contain content that flashes more than 3 times a second, unless the flashes take up a small enough section of the screen area.

Why it matters

Intense flashes can cause some users to have harmful seizures if they have conditions like photosensitive epilepsy.

How to check

Check if anything flashes more than 3 times per second. If in doubt, fail it.

Warning users of the flashing content in advance is not enough to pass.

How to test in detail for 2.3.1 Three Flashes or Below Threshold

Common mistakes

Flashing colours in content

For example, a promotional video contains rapidly flashing colours to get attention from users. The colours take up the whole screen and flash 5 times per second.

This would fail as it could cause seizures.

It can be fixed by reducing the flashing colours to 3 or less per second, or by removing the flashing colours completely.

Good example

Slow changes in colour

For example, a promotional video shows a few different colours. One colour is shown per second.

This would pass. It should not cause seizures.

Non-interference

This is one of four special criteria which all content on a page needs to meet, even if it is normally out of scope of an audit (such as adverts or other third party content). These are referred to as “non-interference” criteria because content must not interfere with the rest of the page. The official standard has more detail about non-interference.

1.4.2 Audio Control (A) is another non-interference criterion which requires that autoplaying audio can be controlled or stopped.
2.2.2 Pause, Stop, Hide (A) is another non-interference criterion which requires a way to stop content that updates frequently, blinks or scrolls automatically.

Useful resources

Read the guidance on photosensitive epilepsy from Epilepsy Action.

Last updated

This page was last updated in October 2026.