WebAIM - Web Accessibility In Mind

Web Content Accessibility Guidelines

WebAIM Accessibility Testing Services

The experts at WebAIM can audit your web site and provide a detailed report to help you remediate accessibility and WCAG compliance issues.


A WCAG 2 Checklist is available for developers to use in implementiation and verification of conformance.


The W3C's Web Accessibility Initiative

Web Accessibility Initiative logo The W3C is an international, vendor-neutral group that determines protocols and standards for the web. Within the W3C, the Web Accessibility Initiative (WAI) and its working groups develop accessibility guidelines for web browsers, authoring tools, evaluation tools, and web content, to name a few. The Accessibility Guidelines Working Group creates guidelines called the Web Content Accessibility Guidelines (WCAG).

WCAG 1.0

WCAG 1.0, finalized in 1999, was a major development in making web content more accessible to people with disabilities. Its 14 guidelines and numerous checkpoints formed the basis for the initial Section 508 guidelines.

As technologies advanced, WCAG 1.0 became less relevant, and the development of WCAG 2.0 began.

WCAG 2.0

WCAG 2.0, released in 2008, shifted emphasis from technique-centered checkpoints to guidelines and success criteria rooted in four core principles:

  • Perceivable
  • Operable
  • Understandable
  • Robust

These principles (sometimes referred to as "POUR") remain constant as technology changes. Each principle contains guidelines, which in turn contain various success criteria. The principles are examined in depth in Constructing a POUR Website.

The Current Standard: WCAG 2.2

WCAG 2 has been updated twice, to sub-versions 2.1 (in 2018) and 2.2 (in 2023). These sub-versions did not replace WCAG 2.0 in the same way that WCAG 2.0 replaced 1.0. Instead, each added new success criteria. Sub-version 2.1 notably added much in the area of mobile devices. The four core principles from 2.0 remain unchanged, as do most success criteria.

Levels of Conformance

To help development teams prioritize accessibility implementation and remediation efforts, WCAG success criteria are organized into three levels of conformance:

  • Level A is a basic requirement for some users with disabilities to be able to access and use web content.
  • Level AA indicates overall accessibility and removal of significant barriers to accessing content.
  • Level AAA provides improvements and enhancements to web accessibility for some users with disabilities.

These levels are cumulative. To claim Level AA conformance, a website must meet all Level A and AA success criteria. Likewise, Level AAA conformance implies that all success criteria from all three levels have been met.

Most websites should aim for Level AA conformance. Depending on the target users, some Level AAA success criteria such as Reading Level, Contrast (Enhanced), Target Size, or others may be beneficial to implement. Very few websites can claim full Level AAA conformance—not even webaim.org or the WCAG website itself!

Conformance Claims

The W3C-WAI outlines a recommended process to claim conformance to one of the levels above. This optional process is based on self-assessment and does not imply certification by the W3C. Third-party organizations like WebAIM can also evaluate a website and certify conformance.

The Future

WCAG 2.n

WCAG 2 continues to be updated. Additional success criteria are being developed for a future WCAG 2.2 and further sub-versions of WCAG 2.

The Silver Project

The Silver Task Force grew out of the early WCAG 2.1 project, because a group of people wanted to work on the next major evolution of accessibility guidance using a user experience model. This meant researching what users needed from accessibility guidance and potentially recommending a major restructuring for WCAG 3.0.