The Web Content Accessibility Guidelines (WCAG) are developed by the World Wide Web Consortium (W3C) through its Web Accessibility Initiative (WAI). First published in 1999 (WCAG 1.0), revised in 2008 (WCAG 2.0), again in 2018 (WCAG 2.1), and most recently updated in 2023 (WCAG 2.2), they have become the international reference standard for web accessibility. Whether you are building for the US, UK, EU, Canada, or Australia, WCAG — at Level AA — is what almost every jurisdiction's accessibility laws require or point toward.
The four POUR principles
All WCAG criteria are organised under four core principles, known by the acronym POUR:
Perceivable — information and user interface components must be presented in ways users can perceive. This means providing text alternatives for images, captions for videos, sufficient colour contrast, and the ability to resize text without loss of functionality.
Operable — all functionality must be operable through a keyboard alone (not just a mouse), and users must have enough time to read and use content. This prohibits keyboard traps, requires visible focus indicators, and mandates that users can navigate without a mouse.
Understandable — content and interfaces must be understandable. This covers readable language, predictable navigation, clear form instructions, and meaningful error messages that tell users how to fix mistakes.
Robust — content must be interpreted reliably by a wide variety of user agents, including current and future assistive technologies such as screen readers, braille displays, and voice control software. This primarily means using valid, semantic HTML.
The three conformance levels: A, AA, and AAA
WCAG criteria are divided into three conformance levels:
- Level A — the minimum level. These criteria address the most severe barriers. A website that fails Level A criteria is essentially unusable by some disabled users. All websites should meet Level A as a baseline.
- Level AA — the standard required by most laws and frameworks, including ADA (US), Equality Act (UK), EAA (EU), AODA (Canada), and DDA (Australia). It addresses the most significant barriers without being overly burdensome. This is the target for most organisations.
- Level AAA — the highest conformance level. Not achievable for all content types and not universally required by law, but aspirational for organisations that prioritise accessibility. Some AAA criteria (such as sign language for all audio content) are impractical for most websites.
What WCAG 2.2 adds over 2.1
WCAG 2.2, published in October 2023, adds nine new success criteria at Level A and AA, focused primarily on cognitive accessibility, mobile accessibility, and focus management. Key additions include: Focus Appearance (visible focus indicator requirements are more specific); Dragging Movements (all drag operations must also be achievable by a single pointer); Target Size (interactive targets must be at least 24x24 CSS pixels); and Accessible Authentication (verification processes must not require users to identify objects or transcribe text). WCAG 2.2 is backwards compatible with 2.1 — meeting 2.2 AA satisfies 2.1 AA requirements. Most regulators are transitioning their technical standards to reference 2.2 over 2024-2026.