Flash Check: WCAG 2.3.1 Tester

Records a web page and reports whether it fails WCAG 2.2 SC 2.3.1 Three Flashes or Below Threshold (general and red flash).

Flash Check records a web page while you use it and tells you whether it fails WCAG 2.3.1, Three Flashes or Below Threshold. It checks both general flashes and red flashes using the WCAG 2.2 definitions, shows where on the page each failure happened, and names the elements most likely causing it. It is built as a modern replacement for PEAT, which uses the older WCAG 2.0 math and needs a video file. Flash Check tests live pages directly in Chrome. HOW TO USE 1. Open the page you want to test. Size the window and zoom the way a user is most likely to view it. 2. Select the Flash Check button in the toolbar. 3. Choose a recording length and select Start test. 4. Play every video, carousel, and animation on the page. You can close the popup; recording continues and the toolbar badge counts down. 5. Do not scroll until the test ends. Scrolling can look like flashing. 6. When the test ends, the badge shows FAIL, PASS, or ? (needs review). The report opens in a new tab and failing areas are outlined on the page. WHAT THE REPORT SHOWS - A verdict: Fail, Pass, or Needs review - Each failure's time range, flashing area, flash rate, and location on the page - A still frame with the failing area outlined - Likely source elements, as CSS selectors - A chart of flashing area over time, with a table view - Videos, animations, and other possible flash sources found on the page - Export as JSON, copy a text summary, or print WHAT IT MEASURES - General flash: a change in relative luminance of 0.1 or more, where the darker state is below 0.80 - Red flash: a change of more than 0.2 in CIE 1976 u'v' color, where one state is saturated red (WCAG 2.2 definition) - Fails when an area flashes more than 3 times in any one second and covers more than 25% of any 341 by 256 CSS pixel area PRIVACY Flash Check never replays the recording and sends nothing anywhere. Results stay in your browser. LIMITS Flash Check tests only what was on screen during the recording, at that window size and zoom. Some protected video records as black and cannot be tested. Results support an expert review and are not a medical safety guarantee. Help and bug reports: https://github.com/jasonday/Flash-Check-WCAG-2.3.1-Tester/issues