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The Web Content Accessibility Guidelines 2.1 (WCAG 2.1), published by the World Wide Web Consortium (W3C), build on and extend WCAG 2.0, which are the most widely-known and adopted web accessibility standards. Most country-specific accessibility standards are currently based on the WCAG 2.0 and related bodies of work. WCAG 2.0 and 2.1 (collectively referred to below as WCAG 2) explain, in broad terms, how to make web content more accessible to a wider group of people with disabilities. When a website meets the WCAG 2 standards, users with disabilities will generally have access to the same functionality and information as the users without disabilities. The WCAG requirements are referred to as “success criteria.”

Version 1.0 of the WCAG was first published in 1999, WCAG 2.0 was published in 2008, and WCAG 2.1 was published in June 2018. Some examples of web-based content where WCAG is applicable include:

  • HTML pages
  • Scalable Vector Graphics
  • Flash
  • PDF documents
  • Silverlight
  • Mobile websites.

The WCAG standards can be applied to other technologies such as software and native mobile apps.  Non-normative documents have been provided to assist people in applying WCAG to non-web ICT and applying WCAG and other WAI standards to mobile technologies.

There are a total of 13 web accessibility guidelines (12 in WCAG 2.0) organized under four principles of accessible design:

  • Perceivable: Able to be seen by a person with visual impairments (through a screen reader, screen magnifier, or other assistive technology), or heard by a person who is hard of hearing or deaf (through captions, written transcript, etc.).
  • Operable: The technology can be operated by a user with a disability, for example, a website can be navigable by keyboard shortcuts for someone unable to use a mouse.
  • Understandable: The technology can be operated by users with varying cognitive abilities.
  • Robust: The technology is compatible with current assistive technology and is prepared to upgrade for future iterations of AT.

It is worth noting that the WCAG guidelines are meant to provide general guidance on implementing web accessibility best practices. The web accessibility guidelines themselves acknowledge that real-world implementation strategies will vary from instance to instance. The WCAG working group provides guidance documents such as sufficient techniques known to meet success criteria and be accessibility supported and known failures which are techniques that are known to fail success criteria.

WCAG 2 Levels

The WCAG 2 success criteria are broken up into three levels:

  • Level A – This level defines the lowest or minimum level of accessibility. Many groups of users with disabilities will find it very difficult or impossible to access information in the document. Satisfying these success criteria is the minimum set of requirements.
  • Level AA – This level defines a higher level of accessibility.  One or more groups will find it difficult to access information in the document. Satisfying these success criteria will remove significant barriers to accessing web content.
  • Level AAA – A web content developer may satisfy these highest level of success criteria. Satisfying these criteria will enhance the user experience for individuals with disabilities.  Not all Level AAA success criteria can be addressed for all types of content.

Web Accessibility Standards generally contain the WCAG 2.0 Level A and AA success criteria and conformance requirements with some movement toward adoption of WCAG 2.1 in specific regions by adoption of WCAG 2.1 into the European Standards EN301-549.

A quick Guide to the Web Content Accessibility Guidelines (WCAG)


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