Operable · 2.3 Seizures and Physical Reactions
Nothing on a page may flash more than three times in any one-second period, whatever the size, brightness or color of the flash. Unlike 2.3.1, there is no threshold exception.
Live demo
The same task, done two ways: switch between the version that passes and the one that fails, or put them side by side. Everything in the box is live, so try it with a keyboard, a pointer or a screen reader.
Compare the one-second strips for both versions: the light is tiny in both, but at this level only the number of flashes counts. Nothing here flashes.
In a video call, a recording light about 24 by 24 pixels blinks between white and dark grey twice a second.
Viewed at 1024 by 768, it covers less than 1 percent of a 10 degree field of vision.
In a video call, a recording light about 24 by 24 pixels blinks between white and dark grey five times a second.
Viewed at 1024 by 768, it covers less than 1 percent of a 10 degree field of vision.
The tools follow the version you last used.
What happened
Why it passes
Two flashes a second is within the limit of three, so the light passes whatever its size or color.
Why it fails
Five flashes a second fails at this level even though the light covers less than 1 percent of a 10 degree field. There is no size exception here.
Examples
Four examples, each one running: the usual ways this criterion fails, and code that passes. Listen to them, measure them, or copy the code.
Fails
Live preview
/* 12 by 12 pixels, five flashes a second */.rec-light { width: 12px; height: 12px; border-radius: 50%; animation: rec-blink 0.2s infinite;}@keyframes rec-blink { 0%, 49% { background: #ffffff; } 50%, 100% { background: #333333; }}The light is far too small to cross the Level A thresholds, but at AAA anything that flashes more than three times in one second fails.
Passes
Live preview
.rec-light { width: 12px; height: 12px; border-radius: 50%; animation: rec-blink 1s 4;}@keyframes rec-blink { 0%, 49% { background: #ffffff; } 50%, 100% { background: #333333; }}One flash a second is within the limit of three (technique G19). Stopping after four seconds also keeps the blinking under the five seconds that 2.2.2 allows without a pause control.
Fails
Live preview
// .is-bright switches the icon between white and dark greysetInterval(() => { liveIcon.classList.toggle("is-bright");}, 100);A flash is a pair of opposing changes, so switching every 100 milliseconds gives five flashes a second, which fails at any size.
Passes
Live preview
<span class="recording"> <span class="rec-dot" aria-hidden="true"></span> Recording</span>A steady dot next to the word Recording shows the state without any flashing, and the word also helps people who cannot tell the color.
Why it matters
It removes flashing risk entirely for people with photosensitive epilepsy and other seizure disorders, including people sensitive to small flashes that fall below the Level A thresholds.
W3C: Understanding 2.3.2Level AAA
Level AAA is the highest level. It is not required for whole sites, but it is worth meeting where you can.
Where it is required
No law on this site requires Level AAA criteria for whole sites.
How to test
A few concrete steps. Automated tools find some failures; most need a person.
Common failures