Here are a number of accessibility validation tools that are available both on-line and in some cases in downloadable format. I have used all of these and don't really have a preference since they all do things in slightly different ways. Not all are equal. Their recommendations can create a certain amount of challenges in terms of getting your pages to "pass". Sometimes these validators will provide conflicting information. It should also be noted that the term "validation" is bit of a misnomer. Some accessibility experts contend that there is no software that can accurately and consistently test HTML or CSS pages. I don't believe that they view the software as useless - just caution the user to realize that this is a tool that doesn't not do a complete job and you as the designer should not become complacent.
As a first step, your pages are going to need correct DOCTYPE information and ideally should be validated for correct HTML and CSS first. The following are all free on-line services.
An easy solution is to install the AIS Web Accessibility Toolbar which is installed in your browser (IE only) and has links to many of these validation tools.
Now, there is a similar Accessibility Toolbar for Mozilla/FireFox! Download the Mozilla-Firefox accessibility extension which provides testing for Section 508 and WCAG related requirements.
There is also a beta version of a new tool called the Functional Accessibility Evaluator that tests for functional accessibility features of web resources related to Section 508 and WCAG.
Both of these tools are under development and would be interested in feedback.
The WebABLE Accessibility Monitor is a fee-based online service, made possible by a partnership between the WebABLE, a Web accessibility portal, and Hi Software, the makers of the AccVerify evaluation and repair software. This service provides scheduling of monitor services, customizable reports, email alerts, W3C WAI and Section 508 reporting and other features. It can monitor entire sites.
More information is available at accessibilitymonitor.com
Commercial site providing services to make web sites accessible.
Information about InFocus can be found on the SSB Technologies site
Commercial site providing services to make web sites accessible.
Information is available at Hi Software.com
Commercial site providing services to make web sites accessible.
Information is available from NetCentric Technologies
Commercial site providing services to make web sites accessible.
Information is available from Deque
* This info borrowed from the WebAIM site and the WAI site.
revised: 10/14/2008