Z-Thru

Check local HTML files for accessibility issues on the page, with built-in guidance. Works offline; nothing leaves your computer.

Z-Thru checks HTML files you open straight from your computer for accessibility issues, without a server, publishing, or an internet connection. Open the inspector over the page you are building and choose Check page. Z-Thru lists what it finds, most severe first: critical in red, serious in orange, moderate in yellow, minor in blue-gray. Select an issue and the page dims around the exact element, with an explanation of the issue, why it matters, how to fix it, and a code example. Edit your source, refresh, and check again to confirm the issue is gone. Runs only when you ask. Nothing checks in the background. Contrast issues show the measured text and background colors and the ratio against the required one, so you can see exactly why. Checks the whole page: scrolls through it to include content that fades in or loads as you scroll, then returns you to where you were. Works offline. Nothing leaves your computer: no accounts, analytics, or AI services. WCAG 2.0, 2.1, and 2.2 A/AA rules, powered by the open-source axe-core engine. A separate Needs human review section for checks no automated rule can make, like keyboard order and meaningful image descriptions. Dock the inspector to either edge or float it; it covers the page without resizing it. Adjustable text size. Latest results saved per file on your computer, with one-click deletion. After installing, open the extension's Details and turn on "Allow access to file URLs". Automated checks find many common problems but cannot establish that a page is accessible. Z-Thru keeps what it tested, what it could not test, and what you must review yourself clearly separate.