The Accessibility DevTools extension for Chrome provides a helpful audit for discovering accessibility issues, including issues within Shadow DOM. It’s powered by the Accessibility DevTools module and a CLI is available that also uses this work for continuous integration audits.

　　Tenon.io — useful for testing common accessibility problems. Tenon has strong integration support across build tools, browsers (via extensions) and even text editors.

　　You can examine the way that assistive technologies see web content by using Accessibility Inspector (Mac), or Windows Automation API Testing Tools and AccProbe (Windows). Additionally you can see the full accessibility tree that Chrome creates by navigating to chrome://accessibility.

　　The best way to test for screen reader support on a Mac is using the VoiceOver utility. You can use ⌘F5 to enable/disable, Ctrl+Option ←→ to move through the page and Ctrl+Shift+Option + ↑↓ to move up/down tree. For more detailed instructions, see the full list of VoiceOver commands and the list of VoiceOver Web commands.

　　tota11y is a useful visualiser for assistive technology issues built by Khan Academy. It’s a script that adds a button to your document that triggers several plugins for annotating things like insufficient contrast ratio and other a11y violations

　　ally.js (by Rodney Rehm) is a library that tries to simplify adding a few accessibility features to your app. It helps query the DOM for all focusable or tabbable elements, traps focus to specific DOM sub-trees, helps determine how focus has changed and comes with several other helpers.

　　On Windows, NVDA is a free, open source screen reader which is fully featured and rapidly gaining in popularity. However, note that it has a much steeper learning curve for sighted users than VoiceOver.

　　ChromeLens helps develop for the visually impaired. It’s also got great support for visualising keyboard navigation paths

　　ChromeVox is a screen reader which is available as a Chrome extension, and built in on ChromeOS devices. However, it currently doesn’t read content in Shadow DOM.