Level A, AA and AAA are WCAG's three conformance levels, and they stack. Meeting AA means meeting everything at A as well, which is why nobody claims the two separately. At WCAG 2.2 that works out at 31 criteria at Level A, 24 at AA and 31 at AAA, so 86 in all and 55 in the set an audit aimed at AA tests against. Level A is the floor, and the criteria there tend to be the ones where assistive technology cannot make up for what is missing. Level AA is what the laws and the contracts name, near enough without exception. Level AAA is an enhanced set that W3C advises against requiring across a whole site, in a note attached to the conformance requirements. The reason it gives is plain. Some content cannot satisfy all of it. So when a law, a client or a lawsuit says WCAG compliant, they almost always mean Level AA. Reading it as anything else costs you money in one direction or credibility in the other.
In practice
Two things about the level system catch people out and neither is about which criteria sit in which tier. Conformance is judged on whole pages and you cannot carve a bit out, so a claim about a page with one broken widget is a claim about a page that does not conform. And responsive variants count as part of the same page, so a site that passes on a desktop and fails at phone width has not passed.
The other one is processes. Where a page is a step in a sequence somebody has to complete, every page in that sequence has to conform at the level claimed. A person cannot skip the step that does not work. That is what makes page sampling risky for anything transactional, and it is why the fourth step of a checkout deserves more attention than ten representative pages.
Aiming above your level is encouraged and worth saying out loud. Conformance is only ever claimed at a level, and authors are invited to report progress against criteria beyond it. A site at AA that also meets several AAA criteria can say so rather than hiding it.
Why it matters
Aiming at Level A leaves you below what almost every obligation naming WCAG asks for. Aiming at AAA across a whole site is a target the standard itself says not to set. The useful answer in nearly every real situation is AA. Where that matters most is in a contract. A clause naming WCAG AAA sounds more careful and commits somebody to a bar that cannot be met for some content. The usual result is an expensive argument, or a quiet decision to ignore the clause, which is worse. Write AA into the contract.
What the three actually mean
A is the floor, where a failure tends to lock somebody out entirely, and it holds 31 criteria. AA adds 24 more and is the level the laws name, which puts 55 rules in the set that gets tested. Read the actual instrument before you assume all 55 are in, because a jurisdiction can adopt AA and carve criteria out of it. Ontario does exactly that, leaving out live captions and audio description. AAA is 31 enhanced criteria, useful to reach for a page at a time and not something to require site-wide, because the standard says some content cannot meet all of it.
Where this shows up on the site
Related terms
- WCAGWCAG is the international standard for web accessibility, published by the W3C.
- ConformanceConformance means satisfying all the requirements of a standard, and WCAG has five of them rather than one.
- Success criterionA success criterion is a single testable rule in WCAG, and it is the unit everything else is built from.
- WCAG versions (2.0, 2.1, 2.2)WCAG 2.0 arrived in 2008, WCAG 2.1 in 2018 with rules for mobile, low vision and cognition, and WCAG 2.2 in 2023 with nine more criteria and one removal.
- GuidelineA guideline is the middle layer of WCAG, and WCAG 2.2 has 13 of them sitting between the four principles and the rules anybody is ever tested against.
Knowing the word is the easy part.
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