What is WCAG? Versions, levels and criteria

WCAG, the Web Content Accessibility Guidelines, is the W3C’s technical standard for making web content more accessible to people with disabilities.

The current version, WCAG 2.2, has 86 success criteria under 13 guidelines and four principles. Each criterion sits at Level A, AA or AAA, and a page meets a level when it meets every criterion at that level and below.

Every A and AA criterion, with code that fails and code that passes, is in our WCAG 2.2 checklist. This post explains how the standard fits together.

Who writes WCAG

WCAG is written by the Accessibility Guidelines Working Group, part of the Web Accessibility Initiative at the World Wide Web Consortium (W3C). Each version goes through the W3C process, with public review, before it is published as a W3C Recommendation, the W3C’s term for a finished standard.

WCAG 2.2 is also an ISO standard. In October 2025 the W3C announced that it had been approved as ISO/IEC 40500:2025, which is the same text as the October 2023 version of WCAG 2.2. The W3C expects the December 2024 update to follow as ISO/IEC 40500:2026.

How WCAG is built

The standard’s requirements sit in three layers: principles, guidelines and success criteria. Each criterion carries a level, and of the three layers only the criteria are testable.

A criterion’s number tells you where it sits: 1.4.3 is the third criterion of guideline 1.4, under principle 1. The criteria are what a page is tested against. 1.4.3, for example, requires a contrast ratio of at least 4.5:1 for text and images of text, and 3:1 for large text, with exceptions for logotypes and for incidental text, such as text in an inactive control or pure decoration. Our post on contrast ratios and how to measure them shows how much detail sits behind one criterion.

Around the standard, the W3C publishes supporting material, and two parts of it explain the criteria. The Understanding documents explain each criterion’s intent and who it helps. The Techniques describe ways to meet a criterion, and common failures. Neither sets requirements: a sufficient technique is one way to pass, not the only one, and the W3C updates both without changing the standard. WCAG’s own introduction counts the sufficient and advisory techniques as a fourth layer of guidance, informative rather than required.

What a success criterion looks like in code

A criterion is written so that a page either meets it or does not. 1.1.1 Non-text Content, at Level A, asks that non-text content has a text alternative that serves the equivalent purpose, with a few exceptions. An image link with no text has no accessible name, so a screen reader can only guess, often by reading out the file name or the link address:

<a href="/cart">  <img src="cart.svg"></a>

The alternative says what the link does, not what the picture shows:

<a href="/cart">  <img src="cart.svg" alt="View your cart"></a>

An image used only as decoration takes an empty alt="", so assistive technology skips it. Whether a text alternative serves the equivalent purpose is a judgement, which is why a tool can find a missing alt but a person checks that the text is right.

Levels A, AA and AAA

The levels are cumulative. In WCAG’s conformance section, a page meets:

• Level A when it satisfies every Level A criterion;
• Level AA when it satisfies every Level A and Level AA criterion;
• Level AAA when it satisfies every criterion at all three levels.

Each level can also be met by providing a conforming alternate version of the page. There is no partial level: a page that meets every A criterion and all but one AA criterion conforms at Level A, not AA, provided it meets the other conformance requirements below.

A Level AA target in WCAG 2.2 means 55 criteria: 31 at A and 24 at AA.

How a criterion gets its level

The working group assigns each level after weighing several factors, which the W3C lists in Understanding Conformance. Among them: whether assistive technology can work around a failure, whether the criterion can be met for every kind of content, whether authors can learn to meet it with reasonable training, and whether it limits functionality or visual design. A criterion that nothing can work around and that every site can meet tends to be Level A. One that some content cannot meet, that takes interpretation to judge, and that would need large changes to functionality or design tends to be AAA.

That is also why the W3C does not recommend requiring Level AAA conformance “as a general policy for entire sites”: some content cannot meet every AAA criterion. AAA criteria are still worth meeting where you can. The level is about how widely a criterion can be required, not how much it matters to the people it helps.

What else conformance requires

Meeting the criteria is the first of five conformance requirements. The other four:

• Full pages. Conformance is for a whole page, never part of one, and it includes every layout a responsive page shows at different screen sizes.
• Complete processes. If a page is one step of a process, such as a checkout, every step must conform at that level.
• Accessibility-supported ways of using technologies. Only ways of using a technology that work with users’ assistive technologies and the accessibility features of browsers can be relied on to meet a criterion. Anything provided in a way that does not must also be available in a way that does.
• Non-interference. Anything on the page that does not meet the requirements must not block access to the rest of the page. Four criteria apply to all content on the page for this reason: 1.4.2 Audio Control, 2.1.2 No Keyboard Trap, 2.2.2 Pause, Stop, Hide and 2.3.1 Three Flashes or Below Threshold.

The versions

The versions are backwards compatible: content that conforms to WCAG 2.2 also conforms to 2.1 and 2.0. Later versions add criteria without changing the earlier ones. The exception is 4.1.1 Parsing, which WCAG 2.2 removed as obsolete; the updated WCAG 2.1 text and the WCAG 2.0 errata say to treat it as always met for HTML and XML content. We go through the nine criteria WCAG 2.2 added and why 4.1.1 went.

WCAG 3 is an early draft with a different structure and name, the W3C Accessibility Guidelines. The W3C says it is years from completion. It does not replace WCAG 2, and nothing we know of requires it.

Which version to work to

The W3C encourages you to use the latest version, WCAG 2.2. WCAG 2.0 and 2.1 are still valid W3C Recommendations, and a law, a standard or a contract may name one of them. Because the versions are backwards compatible, working to WCAG 2.2 Level AA also meets the A and AA criteria of 2.1 and 2.0, though a policy that names 2.0 or 2.1 may still expect 4.1.1 Parsing to be tested and reported.

In the EU, WCAG reaches a website through the European standard EN 301 549, which takes in the WCAG criteria at Level A and AA. V3.2.1, the version cited for public-sector sites, uses WCAG 2.1. V4.1.1, published in September 2026, uses WCAG 2.2 and awaits citation. Which one applies to you, and why no version is yet cited under the European Accessibility Act, is in our guide to how WCAG enters the European Accessibility Act.

Outside the EU, laws differ: some name a WCAG version and level, and some name none. We compare the EU, US and Ontario rules and the WCAG version each one uses.

Conformance is not compliance

Conformance is what WCAG defines: a page conforms at a level when it meets every criterion at that level and below, or has a conforming alternate version, and meets the other conformance requirements above. A conformance claim is optional. WCAG says what a claim must contain if you make one, but you can conform without making one.

Compliance is what a law or a contract asks of you. It may name a WCAG version and level, add its own exceptions, set deadlines, or ask for things WCAG does not cover, such as an accessibility statement, or information about how a service meets the requirements. Meeting WCAG is usually the technical core of it, but the law decides what counts, so read the one that applies to you.