What is WCAG?

What does WCAG stand for?

Web Content Accessibility Guidelines. It is published by the World Wide Web Consortium, the same body that standardises HTML, through its Web Accessibility Initiative.

WCAG matters more than its status suggests. It is not a law anywhere. It is a technical standard that laws and procurement policies point at instead of writing their own rules, which is why the same document sits underneath the Americans with Disabilities Act case law, the European Accessibility Act, EN 301 549, Section 508 and Australia’s Digital Service Standard. Meet the standard once and you have answered all of them in technical terms.

How is WCAG structured?

Four principles, thirteen guidelines beneath them, and a list of individually testable success criteria beneath those. The success criteria are the part you actually work with.

The four principles are usually shortened to POUR:

• Perceivable. Content must be available to the senses. Text alternatives for images, captions for video, sufficient contrast, content that survives being resized.
• Operable. Interface components must be usable. Everything reachable by keyboard, no time limits that cannot be extended, no seizure-inducing flashing, targets big enough to hit.
• Understandable. Content and operation must make sense. A declared page language, predictable navigation, error messages that say what to do.
• Robust. Content must work with assistive technology, now and as it changes. Valid names, roles and states, so a screen reader can report what an element is.

Underneath sit the success criteria, written as pass-or-fail statements about a page. 1.1.1 Non-text Content and 1.4.3 Contrast (Minimum) are success criteria. The numbering is stable across versions, so 2.4.7 means the same thing in WCAG 2.0 and 2.2, and criteria are only ever added at a version boundary, never renumbered.

What do the A, AA and AAA levels mean?

They are conformance levels rather than versions, and they nest. Level A is the floor, AA includes everything in A plus more, and AAA includes everything in AA plus more.

• Level A is the minimum. Failing it usually means some group cannot use the content at all: no keyboard access, no alt text, video with no captions.
• Level AA is the practical target. It adds the criteria that make content usable rather than merely reachable: 4.5:1 contrast for body text, visible focus indicators, consistent navigation, text that reflows at 400% zoom. When a law, a buyer or an RFP names a level, this is almost always the one.
• Level AAA is the most demanding, and the W3C itself says it is not achievable for all content. Treat it as a source of good ideas for specific flows rather than a site-wide goal.

Which version of WCAG is current?

WCAG 2.2, published in October 2023, adding nine success criteria to WCAG 2.1. It is backwards compatible, so meeting 2.2 Level AA means you also meet 2.1 and 2.0 at Level AA.

The additions in 2.2 are mostly about focus, pointer input and cognitive load: focus indicators that are not obscured by sticky headers, alternatives to dragging, minimum target sizes, help that stays in the same place, and not making people re-enter information they have already given you. We covered each of them in WCAG 2.2 explained.

There is also WCAG 3.0 in draft, under the name W3C Accessibility Guidelines. It proposes a different model entirely, scoring rather than pass-or-fail. It is years from being a recommendation and is not something to build against today.

How much of WCAG can a scanner actually check?

Less than half, and being specific about that number is more useful than any coverage claim.

Here is the honest version from building one. RedFlag ships 122 rules mapped to 47 of the WCAG success criteria. Of those 122 rules, 96 run automatically and 26 are manual checks or guidance, because the criterion behind them cannot be decided by looking at markup. A machine can tell you an img has no alt attribute. It cannot tell you whether alt="image1" describes anything. It can tell you the DOM order of your focusable elements. It cannot tell you whether that order is logical for the task.

That split is why the two honest positions are “these specific criteria pass automated checks” and “these criteria need a person to look”. Everything else is a coverage claim doing work it cannot support.

There is a practical upside. The mechanically checkable criteria are also the highest-frequency failures. Contrast, missing alt text, unlabelled form fields and broken heading order dominate what real sites get wrong, so automation catches most of the volume even though it reaches under half the criteria. The most common failures and their fixes are almost entirely in the automatable set.

Where should you start with WCAG?

Not by reading it end to end. The specification is long, and the useful entry point is your own pages.

Scan a few of your highest-traffic pages, look at which criteria the findings map to, and fix those. That gives you a real, short list drawn from your own site instead of a standard with dozens of criteria you may never trip. Then do one keyboard-only pass and one pass with a screen reader on your most important flow, which covers the judgement calls no scanner reaches.

Each rule in the RedFlag rules library names its success criterion, so you can work from a finding back to the part of the standard it belongs to rather than the other way around. That is the direction that actually gets pages fixed.

Frequently asked questions

What does WCAG stand for?

Web Content Accessibility Guidelines. It is published by the World Wide Web Consortium (W3C) through its Web Accessibility Initiative, and it is the standard almost every accessibility law and procurement policy in the world points at rather than writing rules of its own.

What is the difference between WCAG A, AA and AAA?

They are conformance levels, not versions. Level A is the minimum, AA adds the criteria most regulations and buyers actually ask for, and AAA is the most demanding and is not expected across a whole site. AA is the practical target for nearly everyone, and each level includes everything below it.

Which version of WCAG should I use?

WCAG 2.2, published in October 2023, is the current recommendation and is backwards compatible. Meeting 2.2 Level AA means you also meet 2.1 and 2.0 at that level. Some regulations still name 2.0 or 2.1 explicitly, so check what your buyer or jurisdiction asks for, but building to 2.2 covers them.

Can a tool tell me whether I meet WCAG?

Not on its own. Automated rules test the parts of WCAG that can be decided mechanically, such as whether an image has an alt attribute or whether a contrast ratio passes. Criteria that depend on meaning, like whether alt text is actually useful or whether focus order is logical, need a person. Any tool claiming full coverage is describing something other than WCAG.