axe is a standard in accessibility testing that is trusted by Google, Microsoft, and several others. axe is available as a Chrome extension, Microsoft Edge (Chromium edition), and an Android application. They also have a web testing API, Android testing API, and Windows testing API.
The browser plugin checks for WCAG 2 and Section 508 accessibility. The extension utilizes the open source library found at:
To get started with axe Pro, watch the following video from Deque: