Accessibility (WCAG)

Accessibility (WCAG) is the set of international standards, published by the W3C as the Web Content Accessibility Guidelines, that define how to make websites and applications usable by people with disabilities. WCAG organizes requirements around four principles and three conformance levels (A, AA, AAA).

The four POUR principles

WCAG structures every success criterion around four foundational principles, known by the acronym POUR. Content must be:

  • Perceivable — information and interface components must be presentable in ways users can perceive, such as text alternatives for images, captions for video, and sufficient color contrast.
  • Operable — all functionality must be available from a keyboard, users must have enough time to interact, and content must not trigger seizures.
  • Understandable — text must be readable, behavior predictable, and input errors clearly identified and explained.
  • Robust — content must be reliably interpreted by a wide range of user agents, including assistive technologies like screen readers, which in practice means valid, well-structured markup.

Every WCAG success criterion belongs to exactly one of these four principles, which makes POUR a useful framework for auditing a product systematically rather than fixing issues at random.

Conformance levels: A, AA and AAA

WCAG defines three conformance levels. Each higher level includes all the requirements of the levels below it. Level AA is the threshold most commonly referenced in procurement, contracts, and public-sector regulation worldwide.

LevelScopeTypical use
AMinimum set of criteria; addresses the most severe barriers (e.g. keyboard access, text alternatives).Baseline only; rarely sufficient on its own for compliance.
AAIncludes all Level A criteria plus stricter requirements (e.g. minimum contrast ratios, consistent navigation, resizable text).The de facto target for most legal and contractual obligations.
AAAIncludes A and AA plus the most demanding criteria (e.g. higher contrast, sign-language interpretation).Aspirational; W3C states it is not recommended as a blanket requirement for entire sites.

Versions matter: WCAG 2.0, 2.1 and 2.2 are each backward-compatible, with later versions adding criteria for mobile, low vision, and cognitive accessibility.

Questions fréquentes

WCAG stands for Web Content Accessibility Guidelines. They are published by the World Wide Web Consortium (W3C) through its Web Accessibility Initiative (WAI). The guidelines provide a shared, technology-neutral standard for making web content accessible to people with disabilities.

The levels represent increasing degrees of accessibility conformance. Level A covers the most critical barriers, AA adds stricter requirements such as color contrast and consistent navigation, and AAA is the most demanding. Each level is cumulative, so AA compliance also requires meeting all Level A criteria.

Level AA is the standard most organizations aim for. It is the level referenced by most accessibility regulations and procurement requirements internationally, and the W3C does not recommend AAA as a blanket goal for entire sites because some AAA criteria cannot be satisfied for all types of content.

WCAG itself is a technical standard, not a law. However, many countries and regions reference it directly in their accessibility legislation and public-sector procurement rules, which turns WCAG conformance into a legal or contractual obligation in practice for a large number of organizations.

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