There are a number of tools are available to test pages for accessibility. These can be useful, especially to people who have not handled the more technical aspects of coding and to those who have a large number of pages to check.
How to use testing tools
You should note that although they can help to a great extent, there is currently no way to automate the process in a way that is foolproof. This is simply because the tools themselves can understand the source code, but they cannot understand how the code is being used.
For example, the tool will understand that the page contains a table, but it can not identify whether it is being used for layout or to display data. This can be an issue because different standards and techniques apply to the two different types of tables. Another example is the use of colour and contrast. A checking tool could prompt you on these issues, but essentially accessible use of colour and contrast is about good judgement on behalf of the designer.
A certain level of manual intervention is still required in most cases to either guide the tool itself, or once it has diagnosed an accessibility problem, to change the source code of your web pages by hand. These tools can help, but they should always be used in conjunction with solid design skills and a good level of user testing.
Validation
One of the best ways to start accessibility checking is to ensure that the code you have created is valid and conforms to World Wide Web Consortium (W3C) standards. If your source code is properly validated before running accessibility checks with the tools listed below, then it will filter out a large number of the issues that may be flagged by an accessibility checker. This means that once you are sure the code is valid, the reports you get back from your accessibility checker will be smaller and easier to work with.
A number of the more common "What You See Is What You Get" (WSIWYG) web editors have the ability to control the type of code that is produced. To ensure that all is well however you should run the source code through a validator. There are a number of validators on the market to choose from, so choose the one that suits your requirements.
A free markup validation service is available in both online and downloadable versions from the W3C themselves.
Wave
Wave is a free online web accessibility evaluation tool provided by WebAIM. It can be used to evaluate single pages, and shows the results directly on screen, displayed on top of the evaluated page. Wave allows testing of live pages, uploaded local files or you can copy/paste HTML code.
This tool can also be installed on Firefox as a toolbar, allowing evaluation of pages off-line, including password protected, secure, or otherwise sensitive web content.
aDesigner
aDesigner is a free diagnostic and simulation tool created by IBM engineers and now part of the Eclipse Accessibility Tools Framework (ACTF) project.. It can be downloaded and once installed, will check online or local pages, against the WCAG 1.0 guidelines, Section 508, the Japanese Industrial Standard and more. Pages are also rated by compliance, how easy they would be to listen to and navigate.
aDesigner is also capable of simulating different sight conditions, such as low vision and colour deficiency. The interface is divided in panels and modified pages can be previewed side-by-side with the original.
Deque Worldspace Free Analysis tool
Worldspace is an on-line, single page compliance checker that can test pages to any level of WCAG 1.0 or Section 508 conformance. The report is laid out in tables giving a description of each problem, the conformance level failed by examples, the code creating the problem and its line number in the HTML.
The online report may be very long on pages with lots of issues, but for those with just a few problems, this may be easier to digest than other single page reports.