What is WCAG

What WCAG is, in one paragraph

WCAG, the Web Content Accessibility Guidelines, is the technical standard for making websites usable by people with disabilities. It is written by the World Wide Web Consortium (W3C), the web's main standards body, through a working group of its Web Accessibility Initiative. W3C's stated aim is a single shared standard for individuals, organisations and governments everywhere, and it is the yardstick that US rules, procurement contracts and audit reports point to.

It is a technical document, not a law and not a beginner's guide. It sets testable rules, called success criteria, for the text, images, sounds and code of a page. Whether you must meet it, and which version, depends on who you answer to, which is the part people mix up; that is covered below under Level AA. The same rules can be applied to PDFs and other documents too, as how to make a PDF accessible shows.

The four principles: perceivable, operable, understandable, robust

Everything in WCAG 2.2 hangs from four principles, often shortened to POUR. Under them sit 13 guidelines, and under the guidelines sit the success criteria, the only part you are tested on. The principles are the quickest way to see what the standard cares about: whether people can take in the content, use it, understand it, and reach it through the tools they rely on.

The counts show where the work sits for a small business site. Perceivable and operable carry 40 of the 55 Level A and AA criteria between them, and most of the problems owners fix first live there: missing alt text, low contrast, menus that a keyboard cannot open. Robust carries two, but they matter to every custom button and pop-up on the page.

Levels A, AA and AAA

Every success criterion has a level. The levels stack: Level AA means meeting every A criterion and every AA criterion, 55 in WCAG 2.2, and Level AAA means meeting all three sets. W3C itself does not recommend requiring AAA for a whole site, because some content cannot meet it.

Two rules in the conformance section surprise owners. Conformance is judged on full pages: a page with one inaccessible widget does not conform, even if the rest is perfect. And WCAG does not require you to claim anything; a claim, if you make one, has to give its date, the WCAG version and level, and the pages it covers.

Success criteria, techniques and the Understanding pages

Search for any WCAG rule and you land on one of five W3C documents. Only one of them is the standard. The rest explain it, and W3C is explicit that they are informative: they do not set requirements and you do not need them to conform.

Here is how the four fit together for one criterion, the colour contrast rule:

1. The criterion

   1.4.3 Contrast (Minimum), Level AA: text needs a contrast ratio of at least 4.5:1, large text 3:1.

2. Understanding

   Explains who it helps and that ratios are not rounded: 4.499:1 does not meet 4.5:1.

3. A sufficient technique

   G18 gives a way to meet it: ensure a contrast ratio of at least 4.5:1 between text and its background.

4. Your test

   Measure the colour pair. Meeting the criterion is what counts, by this technique or any other way.

You can run that last step in our contrast check, and the rule itself is explained in colour contrast requirements explained.

Why Level AA is the working target

No single law says “WCAG” for every website. Each rule a business might answer to names its own version, and all of them stop at Level AA:

Federal agencies work to the Section 508 Standards, which use WCAG 2.0 Level A and AA. So the practical target for a small business is WCAG 2.2 Level AA: it covers 2.1 and 2.0 because each version keeps the last one's criteria, and it is the version W3C advises. WCAG 2.2 added nine criteria and removed one, 4.1.1 Parsing; what changed is set out in what changed in WCAG 2.2.

The rules for governments are in the DOJ Title II web rule, the federal ones in what Section 508 is, and what the ADA asks of a private business in ADA compliant website: what the law asks. No federal body certifies a website as ADA compliant: you meet WCAG, test it and, if you choose, say so.

What WCAG 3 is, and what it is not

WCAG 3 is a new standard W3C is still writing. Its full name changes to the W3C Accessibility Guidelines, because it reaches past web pages to apps, tools, publishing and newer technology. The latest Working Draft is dated 10 September 2026, and W3C calls it an incomplete draft that will change; the document itself says it should be cited only as a work in progress.

The draft keeps requirements similar to WCAG 2 but rebuilds the frame around them: outcome statements, core and supplemental requirements, and assertions about the content and about the organisation. Instead of A, AA and AAA, the September 2026 draft has one conformance point, meeting every core requirement, and tags each core requirement by what failing it does to a person (physical harm, risk, a barrier or friction) to report progress in tiers below and above that point. All of that is still under review.

Where to start on this site

If you have read this far, you know the target: WCAG 2.2 Level AA, tested on full pages. These are the quickest ways in, in a sensible order.

• WCAG 2.2 AA checklistAll 55 Level A and AA criteria, each as a plain test, with a printable record.
• Contrast checkTwo colours in, the ratio out, against 1.4.3 and 1.4.6.
• Alt text checkOne image's alt text checked against what the image does, for 1.1.1.
• Focus order checklistA guided walk with the Tab key: skip link, menu, visible focus, traps.
• How to make a website ADA compliantThe order to do the work in, from a first test to a fixed and recorded site.

If you would rather hire the testing out, the firms that audit against WCAG by hand are compared in WCAG audit services compared, and the official lists of tools and certified testers are in our directory of evaluation tools and auditor lists.

Quick reference

This is general information, not legal advice. For your own situation, ask a lawyer.