Deque Systems makes an open source project called aXe:
The Accessibility Engine for automated testing of HTML-based user interfaces. Drop the aXe on your accessibility defects!
There are a variety of ways you can use it, like a browser extension for Chrome or Firefox. It’s also just a stand-alone library, which is a smart move as it means the functionality of aXe is portable to all these different places.
To use it on a Pen, it’s as simple as including the library, like as an External Resource:
https://cdnjs.cloudflare.com/ajax/libs/axe-core/2.4.2/axe.min.js
Then calling it in your JavaScript:
axe.run(function(err, results) {
console.log(results.violations);
});
Here’s an example Pen where you can see it find errors.