WAVE by WebAIM
WAVE is a web-based tool to help web developers make their web content more accessible. WAVE is not a substitute for human evaluation. In fact, no automated tool can be, because web accessibility is best evaluated subjectively. Although WAVE helps users learn about web accessibility, it is most effective when used by someone knowledgeable about web accessibility. WAVE facilitates this kind of subjective evaluation by exposing many kinds of accessibility errors in the content, as well as possible errors, accessibility features, semantic elements, and structural elements. Once these elements are exposed, knowledgeable web developers can decide what changes need to be made, if any.
People who are not web accessibility experts can also benefit from WAVE by referring to the summary report which WAVE displays after processing the page. This report summarizes the number of errors, possible errors, and so on. A quick glance at the Errors, Features, and Alerts view of the report can also be informative, because the icons are color coded with red icons representing errors and yellow icons representing possible errors. Other types of icons also have specific colors assigned to them.
To use WAVE, open a web browser and go to the WAVE home page. Enter the URL of the site you want to check then hit enter/return on your keyboard to have WAVE scan the site.
Other Accessibility Checking Tools
Review the list provided by WebAIM for more options.