What does WCAG 2.1 level AA mean in plain language?

WCAG 2.1 AA means applying four accessibility principles

WCAG 2.1 level AA is the set of technical requirements that determines whether a website and its associated checkout and login flows are usable for people with visual, hearing, motor, or cognitive disabilities. The standard is built around four principles: content must be perceivable (sufficient contrast between text and background, alternative text for images), operable (every function must also work with keyboard only, without a time limit that cannot be adjusted), understandable (clear labels for form fields, consistent navigation), and robust (code must work correctly with screen readers and other assistive technology). Level AA is the middle of three levels — A, AA, and AAA — and is the requirement chosen as the practical baseline in European regulations.

For an online shop, this concretely means things like: can a customer use only a keyboard to add a product to the shopping cart and check out, does a screen reader announce a button as "add to cart" instead of "click here", and is an error message for an incorrectly filled form field also understandable for someone with a reading disability. Some of these requirements can be tested automatically — contrast and missing alternative text, for example — but whether an alternative text actually describes the image, or whether the checkout flow makes sense with only a keyboard, requires human judgment. An automated scan therefore always shows which part has been tested and which part has not; it never indicates that a site fully meets the requirements.

Established in EN 301 549, which refers to WCAG 2.1

The European accessibility directive itself describes no technical details, but refers to the harmonised standard EN 301 549 V3.2.1; that standard builds its web components almost entirely on the success criteria of WCAG 2.1 from the World Wide Web Consortium, at level AA. That is the same technical foundation for all twenty-seven member states, regardless of which national law transposes the directive. A successor, EN 301 549 V4.1.x with WCAG 2.2 AA, is expected in 2026, but does not yet apply as a requirement.