axe DevTools runs Deque’s open-source axe-core rules engine inside the browser, scanning the currently loaded page for WCAG failures like missing alt text, insufficient contrast, and invalid ARIA usage, then reporting each issue with the specific element and a link to guidance on how to fix it.
It is one of the most widely used automated accessibility testing tools in the industry and forms the underlying engine for many other testing products, but like all automated scanners it only catches a portion of real WCAG failures, roughly a third by most industry estimates, so manual testing remains necessary alongside it.