axe-core / Automated Testing

axe-core is an open-source accessibility testing engine, developed by Deque Systems, that programmatically inspects a rendered web page and reports accessibility violations mapped to WCAG success criteria. It is one of the most widely adopted engines in the field and powers the accessibility checks in many browser extensions, developer tools, and continuous-integration pipelines, including scanning products like CompliaScan.

The engine is deliberately conservative. A core design goal of axe-core is to minimize false positives, meaning it aims to only report issues it can determine with high confidence are genuine problems. That reliability is what makes it safe to run automatically on every deploy without drowning teams in noise, but it also means the engine stays silent on anything it cannot verify by rule.

This is the central truth about automated accessibility testing in general: it catches only the machine-testable portion of WCAG, commonly estimated at around 30 to 40 percent of issues. Automated tools excel at detecting missing alternative text, insufficient color contrast, missing form labels, empty links and buttons, invalid ARIA usage, and an undeclared page language. These are high-value findings precisely because they are unambiguous and common.

What automation cannot judge is meaning and experience. Whether alt text is accurate, whether reading and focus order make sense, whether an error message is clear, whether a custom widget actually works with a screen reader, these require human evaluation. The correct role for axe-core and similar engines is as the fast, repeatable first layer of a testing program that also includes keyboard testing and assistive-technology review. Any tool claiming full compliance from automation alone is overstating what is technically possible.