WCAG explained: levels, the 55 criteria and what can be tested

WCAG in brief

The Web Content Accessibility Guidelines (WCAG) are published by the W3C, the body that also writes the standards for HTML and CSS. They describe what makes websites and apps usable for people with disabilities: people who are blind and use a screen reader, people who cannot use a mouse, people with low vision, people who are deaf, and people with cognitive impairments.

WCAG consists of success criteria. Each criterion is a testable statement, such as "text has a contrast ratio of at least 4.5:1" or "all functionality can be operated with the keyboard". Laws rarely write their own technical rules. They point to WCAG, usually through the European standard EN 301 549.

Four principles

The criteria are grouped under four principles:

• Perceivable: information can be seen or heard by everyone, for example through text alternatives for images, captions for videos and enough contrast.
• Operable: everything can be operated, including with the keyboard, with enough time and without content that flashes.
• Understandable: text, navigation and forms behave predictably, and errors are explained.
• Robust: the code is clean enough for assistive technology such as screen readers to read it correctly.

Levels A, AA and AAA

Each criterion has a level:

• Level A covers the most basic barriers. Without it, some people cannot use a page at all.
• Level AA builds on A and is the level laws and standards require. WCAG 2.2 has 31 criteria at level A and 24 at level AA, 55 in total.
• Level AAA is the highest level. The W3C itself does not recommend requiring it for whole websites, because some content cannot meet every AAA criterion.

When someone says a website should "meet WCAG", they almost always mean level AA, which includes all of level A.

WCAG 2.1 or 2.2?

WCAG 2.1 was published in 2018 and WCAG 2.2 in October 2023. Version 2.2 adds six criteria at levels A and AA, among them a minimum size for click targets and rules for logins that do not depend on remembering a password. It also removes criterion 4.1.1 Parsing, which modern browsers have made unnecessary.

The European Accessibility Act does not name a WCAG version itself. The harmonised standard EN 301 549 currently refers to WCAG 2.1 at level AA. A new version of the standard that includes WCAG 2.2 is being prepared.

We test against WCAG 2.2 at level AA. Anyone who meets 2.2 also meets the criteria of 2.1, and is ready for the next version of the standard. In the table below, the six new criteria are marked "New in WCAG 2.2" instead of an EN 301 549 clause.

What can be tested automatically

Some criteria can be measured by a machine: whether an image has an alt attribute, whether a form field has a label, whether text has enough contrast. Others always need a person: whether the alt text describes the image, whether the order of a page makes sense, whether error messages help.

Even where automatic rules exist, a passed rule only means that the rule found nothing. It does not mean that the criterion is met. That is why Luentis works in three layers:

• Automatic rules check every page of the scan.
• Scripted checks test things such as keyboard traps, visible focus and layout at 320 pixels on up to 25 pages of a full scan.
• The guided check asks you, in plain language, about everything a machine cannot judge.

All 55 criteria at levels A and AA

The tables show every criterion of WCAG 2.2 at levels A and AA, with its level, its clause in EN 301 549, and how Luentis checks it. The titles are our translations; the official wording is on the W3C website.

And WCAG 3.0?

The W3C is working on WCAG 3.0, with a new structure and a new way of scoring. It is a draft and will not be final for several years. Laws and standards will keep pointing to WCAG 2.x until then, so WCAG 2.2 at level AA is the right goal today.

How to go about it

1. Check your homepage for free and see which errors the automatic rules find.
2. Fix the errors in your theme or templates, where they affect every page.
3. Answer the guided check for what a machine cannot test.
4. Document the result in an accessibility statement.

The single audit does all of this for up to 250 pages, with every criterion and its status in the report.