Accessibility testing is the process of ensuring that a Web application is accessible to people with disabilities. Accessibility verification can help you prevent functionality problems that could occur when people with disabilities (approximately 19% of the US population) try to access your application with adaptive devices such as screen readers, refreshable Braille displays, and alternative input devices. In addition, if your Web application is produced for or by a US government agency, accessibility verification is required in order to prevent violation of a federal law, the potential loss of government contracts, and the potential for costly lawsuits.

Accessibility testing involves ensuring that your application complies with one (or both) of the two available sets of Web accessibility guidelines:

• Section 508 Web Guidelines: A set of guidelines that detail sixteen specific requirements that a Web site must satisfy to comply with the Section 508 amendment to the Rehabilitation Act, which requires that any technology produced by or for US government agencies must be accessible to people with disabilities. Most of these guidelines focus on ensuring graceful page transformations to a variety of devices and making content understandable and navigable on a variety of devices. Although these guidelines were designed specifically for federal agencies and vendors producing technology for federal agencies, they have become the standard that many Web developers use to gauge site accessibility. To view a detailed explanation of these guidelines, visit www.section508.gov.

• Web Accessibility Initiative (WAI) Guidelines: A set of guidelines developed by a W3C organization committed to making the Web more accessible for people with disabilities. These guidelines are similar to Section 508 guidelines because Section 508 guidelines were largely based on the WAI guidelines. To view a detailed explanation of these guidelines, visit www.w3.org.

Both sets of guidelines generally prompt you to follow design and navigation best practices and add optional or redundant elements to ensure that the Web application functions in a variety of contexts. In fact, following these guidelines not only prevents problems that would affect people with disabilities, but also prevents problems that could impact users on desktop systems, PDAs, Web-enabled phones, kiosks, and other existing and upcoming internet devices.

You can significantly streamline and facilitate the accessibility testing process by using a tool that automatically checks the majority of the Section 508 and WAI guidelines. However, while accessibility testing tools can be a tremendous aid in verifying accessibility, a gold stamp from even the best verification tool does not mean that the application is actually accessible. Some degree of human inspection is always required to guarantee compliance because the criteria for some guidelines are too subjective and/or complex for today's systems to evaluate. For example, machines cannot automatically verify the W3C guidelines "Provide clear and consistent navigation mechanisms – orientation information, navigation bars, a site map, and so on – to increase the likelihood that a person will find what they are looking for at a site."

For both automatic and manual verification, you can save yourself considerable time and grief by starting your testing early in the development process – before accessibility problems have the opportunity to multiply as the result of code reuse or interactions.