WCAG Conformance Levels: A, AA, and AAA

WHY IT EXISTS Not all web content can or needs to meet the absolute highest standard of accessibility. A tiered system was created to accommodate different situations and content types, allowing teams to set practical, clear targets for accessibility conformance rather than facing an all-or-nothing requirement.

THE MENTAL MODEL Think of WCAG conformance like a hotel rating system. To get a three-star rating, a hotel must first meet all one-star and two-star requirements. Similarly, WCAG levels are cumulative: Level AA conformance requires satisfying all Level A criteria first, and Level AAA requires satisfying all A and AA criteria.

HOW IT WORKS Conformance is measured against three levels of success criteria, which are objective and testable rules for accessibility.

Level A: This is the minimum level of conformance. It addresses the most basic and critical accessibility barriers. If a page does not meet Level A, it is not considered accessible.

Level AA: This level includes all Level A criteria plus additional, more comprehensive ones. Level AA is the most common target for organizations and is often the standard required by law.

Level AAA: This is the highest level, including all A and AA criteria plus the most stringent requirements. These criteria are often context-specific and can be impossible to satisfy for certain types of content.

Conformance applies to the full web page, not just a portion of it.

WHEN TO USE IT Use these levels to establish clear, organization-wide accessibility policies. They provide a shared vocabulary and objective criteria for designers, developers, and testers. Many legal frameworks and corporate policies explicitly require conformance to a specific level, most commonly WCAG Level AA.

WHEN NOT TO USE IT The primary footgun is requiring Level AAA conformance as a general policy for an entire website. The W3C explicitly advises against this because it is not possible to satisfy all Level AAA success criteria for some content. It's a target for specific content, not a blanket rule.

ONE CANONICAL EXAMPLE A university website adopts a policy that all public pages must conform to WCAG 2.1 Level AA. This means every page must satisfy all Level A criteria (like providing alt text for images) and all Level AA criteria (like ensuring text has a color contrast ratio of at least 4.5:1). They might aim for Level AAA on a simple text-only policy page, but they do not mandate it for complex pages with interactive media.