Published October 23, 2026

WCAG 2.3.1 Three Flashes or Below Threshold, Level A

Does WCAG allow flashing content?

Only within a strict limit. Success criterion 2.3.1 Three Flashes or Below Threshold is Level A, so it is also required at Level AA. 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. The text is in the W3C WCAG 2.2 Recommendation.

What counts as a flash?

A pair of opposing changes in relative luminance that can cause a seizure when the change is large enough and fast enough. The W3C explanation is in Understanding Success Criterion 2.3.1. Red flashes have a separate threshold because they are higher risk. Content that stays under three flashes per second, or that stays below both thresholds, meets the criterion. Ads, intro videos, and loading animations that strobe past that rate fail. Video that can flash is also covered on the video and audio page.

Is this the same as pausing animation?

No. Success criterion 2.2.2 Pause, Stop, Hide is about moving, blinking, scrolling, or auto-updating content that lasts more than five seconds beside other content. A pause control can meet that rule. It does not make seizure-risk flashing allowed under 2.3.1. Blinking meant to draw attention is 2.2.2. Flashing that can trigger a seizure is 2.3.1. Pausing animation is covered on the pause animation page.

How do you check a page for flashes?

Watch every autoplay region, carousel, and video for rapid brightness changes. Count flashes in one second. A tool rarely proves that content stays under the threshold. A person has to see the sequence, which is why a passing score is not conformance, as covered on the scanner page. If a clip flashes too often, remove the flash, slow it down, or replace it with a version that stays under the limit.

Does the Title II web rule include three flashes?

Yes. The Department of Justice rule for state and local government websites names WCAG 2.1 Level AA. That level includes 2.3.1, which is Level A. Governments with a population of 50,000 or more have until April 26, 2027. Smaller governments and special districts have until April 26, 2028. Who must comply is on the Title II web rule page. Replacing a flashing intro or ad is remediation.