WCAG accessibility guidelines

Definition

WCAG stands for Web Content Accessibility Guidelines, the W3C standard that defines what accessible web content means in testable terms. Rather than describing good intentions, it states success criteria that can be checked and either pass or fail.

The four principles

Everything in the standard sits under four principles, usually remembered as POUR:

Perceivable — information must be presentable in ways people can perceive, which covers text alternatives, captions, and contrast. Operable — the interface must be usable, which covers keyboard access, timing, and navigation. Understandable — content and operation must make sense, which covers readability, predictability, and error handling. Robust — content must work with current and future assistive technology, which is where correct markup and name, role, and value live.

Levels A, AA, and AAA

Success criteria are assigned Level A, AA, or AAA. A conformance claim names the level met and includes every criterion at that level and below. WCAG itself says Level AAA conformance is not recommended as a general policy for entire sites because some content cannot satisfy every AAA criterion. Legal, contractual, or procurement targets vary and must be checked in their own jurisdiction and context.

Versions

2.0 arrived in 2008, 2.1 added mobile, low vision, and cognitive criteria, and 2.2 added several more including focus appearance and accessible authentication. Each version is backwards compatible: meeting 2.2 means meeting 2.1 and 2.0. WCAG 3 remains an incomplete Working Draft. W3C says its requirements will change and that WCAG 2 remains the current standard. WCAG 3 is exploring a different structure, conformance model, and broader scope; do not audit a site as though the draft were a finished replacement.

What conformance does and does not mean

Conformance is a claim about specific criteria, evaluated across whole pages and complete processes rather than fragments. It is not the same as being usable. A page can satisfy every AA criterion and still be confusing, and a page can fail a criterion and remain broadly usable. Treat the criteria as a floor that catches known exclusions, not as a definition of quality.

Automated tools evaluate only a subset of the criteria; the rest require human judgement about whether a name is meaningful or an order is logical.

Common failures

• Claiming conformance based on an automated scan alone.
• Targeting AAA site-wide, against the standard's own guidance.
• Testing isolated components rather than whole pages and complete tasks.
• Treating conformance as the goal rather than as the minimum.

Review question

Pick your page's primary task and walk it against the four principles in order: can everyone perceive the information, operate the controls, understand what happened, and reach it with the assistive technology they actually use? A failure at any principle is a real exclusion regardless of the overall score.