WCAG
Definition
WCAG is a set of testable success criteria published by the W3C's Web Accessibility Initiative. The criteria sit under four principles — perceivable, operable, understandable, robust — and each is graded Level A, AA or AAA. WCAG 2.0 appeared in 2008, WCAG 2.1 added seventeen criteria in 2018 for mobile and low vision, and WCAG 2.2 became the current Recommendation in October 2023, adding nine criteria and retiring one (4.1.1 Parsing). That leaves 2.2 with 86 success criteria: 31 at Level A, 24 at AA and 31 at AAA. Level AA is the practical target, and the W3C says plainly that AAA conformance is not achievable for whole sites. The numbering is positional, so 1.4.3 Contrast (Minimum) is principle 1, guideline 4, third criterion.
Why It Matters
WCAG matters because nearly every accessibility rule in the world defers to it rather than writing its own, starting with ISO/IEC 40500:2012, which adopted WCAG 2.0 Level AA wholesale. The European standard EN 301 549 builds public procurement requirements on it, and the European Accessibility Act has applied to many consumer digital products since 28 June 2025. In the United States, Section 508 was refreshed in 2017 to point at WCAG 2.0 AA, and a 2024 Department of Justice rule sets WCAG 2.1 AA for state and local government web content with deadlines in 2026 and 2027 depending on population. Naming a version therefore matters: a contract that says only 'WCAG compliant' is unenforceable, because it does not say which version or which level. This is the general shape of the rules and not legal advice.
How It Works
Each success criterion is written to be pass or fail by a tester, and comes with three companion documents: Understanding, Techniques and the How to Meet quick reference. Levels are cumulative — AA conformance means meeting every A and AA criterion, not just the AA ones. Conformance is claimed for full pages, never for parts of a page, and for complete processes, so a checkout that fails on step three fails as a whole. Two further conditions are easy to miss: content must rely on accessibility-supported technologies, and non-conforming versions of content must not interfere with the conforming ones. A claim names the version, the level, the date, the pages covered and the technologies relied on.
Real-World Example
A consultancy is asked to deliver a research report as a web page, and the contract says WCAG 2.2 Level AA. They publish it at insight-report.99helpers.site as a single HTML file with a proper heading structure, alt text on four charts, body text at 7:1 against white and a visible focus ring on every link. Two criteria added in 2.2 come into play: 2.4.11 Focus Not Obscured (Minimum), because the sticky header was hiding focused links, and 2.5.8 Target Size (Minimum), because the footer icons were 18 by 18 pixels rather than the 24 by 24 the criterion asks for. Both are fixed in CSS before publishing.
Common Mistakes
- ✕Writing 'WCAG compliant' with no version or level — the phrase covers everything from 2.0 Level A to 2.2 Level AAA, which are very different amounts of work
- ✕Chasing Level AAA across a whole site — the W3C itself states that full AAA conformance is not possible for all content, so it is better used criterion by criterion where it helps
- ✕Claiming conformance for a template rather than for the published pages — conformance is a claim about full pages and complete processes, and one broken step breaks the claim
Related Terms
Web Accessibility
Web accessibility is the practice of building pages, documents and media that people with disabilities can perceive, operate and understand — including people using a screen reader, a keyboard alone, screen magnification or captions.
Colour Contrast
Colour contrast is the difference in luminance between text and the surface behind it. WCAG asks for at least 4.5:1 for normal text and 3:1 for large text at Level AA.
Keyboard Navigation
Keyboard navigation is operating a page without a mouse: Tab and Shift+Tab to move between controls, Enter and Space to activate them, arrow keys inside composite widgets such as menus and radio groups.
EN 301 549
EN 301 549 is the European standard setting accessibility requirements for ICT products and services, and it is what public-sector procurement across the EU points at. For web content it adopts WCAG wholesale rather than inventing its own rules.
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