Axe Core

Axe is an accessibility testing engine for websites and other HTML-based user interfaces. It's fast, secure, lightweight, and was built to seamlessly integrate with any existing test environment so you can automate accessibility testing alongside your regular functional testing.

Axe-core has different types of rules, for WCAG 2.0 and 2.1 on level A and AA, as well as a number of best practices that help you identify common accessibility practices like ensuring every page has an h1 heading, and to help you avoid 'gotchas' in ARIA like where an ARIA attribute you used will get ignored.

With axe-core, you can find on average 57% of WCAG issues automatically. Additionally, axe-core will return elements as 'incomplete' where axe-core could not be certain, and manual review is needed.