Q2 of 24 · Accessibility
What is the difference between WCAG conformance levels A, AA, and AAA?
Short answer
Short answer: Level A is the bare minimum — failures block users entirely. Level AA is the legal and practical target for most products, covering contrast ratios, keyboard access, and captions. Level AAA includes criteria that are often impractical for entire sites, such as sign language for all video content.
Detail
WCAG organises success criteria into three levels based on impact and feasibility:
Level A (24 criteria in WCAG 2.1): the most critical failures — things that completely block access for a group of users. Examples: non-text content has no alternative (1.1.1), keyboard functionality is blocked (2.1.1), there is a time limit with no way to extend it (2.2.1). Failing a Level A criterion means some users literally cannot use the feature.
Level AA (20 additional criteria): the practical compliance target referenced in most legal standards (ADA settlements in the US, Section 508, EN 301 549 in the EU). Examples: minimum contrast ratio of 4.5:1 for normal text (1.4.3), no keyboard trap (2.1.2), language of page is identified (3.1.1), error suggestions are provided (3.3.3). Most product teams target AA as a baseline.
Level AAA (28 additional criteria): aspirational requirements that are often impossible to satisfy for entire sites. Examples: sign language interpretation for all prerecorded audio (1.2.6), contrast of 7:1 (1.4.6), no timing on any interaction (2.2.3). These are appropriate as targets for specific content types (e.g. a government sign language service) not as site-wide mandates.
For testing purposes: your test plan should explicitly target AA. Treat A failures as critical (block release on public-facing flows), AA failures as high, and AAA failures as aspirational if time permits.