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The Problem With Automated Accessibility Testing Tools
An automated accessibility tool is a piece of software which can test a web page, or even an entire website, for accessibility. Automated accessibility tools are useful because they can save you a huge amount of time. Don't want to check images for alt text on each and every page on your website? Run the site through an automated tester and it'll do it all for you!
Automated accessibility testing tools have been around for a long time and have historically been a useful way of checking websites for accessibility. Bobby, one of the first and most well-known automated accessibility testing tools, is now almost 10 years, and although is no longer freely available, plenty of other free tools such as WebXact (http://webxact.watchfire.com/) and Wave (http://wave.webaim.org/index.jsp) do exist.
But are these tools a little too good to be true? Can you test a website for accessibility so easily? Unfortunately the answer is a resounding no. There are a number of underlying problems associated with using just automated tools to test for accessibility:
Literal interpretation of guidelines
Any automated accessibility testing tool, being a piece of software, doesn't have very much in the way of common sense. It will interpret each and every accessibility guideline literally, without bearing any other thought to what else is on the page.
The definition of the word guideline, according to Dictionary.com, is "a rule or principle that provides guidance to appropriate behaviour". A guideline simply offers guidance to what the best practice is - it shouldn't just be applied without regard to other factors.
For example, one of the W3C accessibility guidelines states that a table summary should be provided for all tables. (This summary doesn't appear on the screen, but it's read aloud to screen reader users before reading through the table content.) Table summaries are useful as they tell screen reader users what to expect in the table. However, there may be a heading directly before the table and it describes what the table is about. In this instance, this summary is essentially useless as it will just repeat what the previous heading said.
Can't check any content issues
The way that content is structured both on the page and across the website is a massive part of accessibility. A website may be perfectly coded and conform to the highest coding standards. If its content is poorly structured though, the site will prove difficult to impossible for some special needs web users.
There are a number of important accessible content considerations, none of which automated accessibility testing tools can check for. Some of these important considerations include:
Can't check many coding issues
The vast number of accessibility guidelines tend to be related to how the site is coded. Automated accessibility testing tools are unfortunately unable to test for many of these too. Examples of HTML-related accessibility considerations which these tools can't check for include:
Outdated guidelines are used
Automated accessibility testing tools generally use the W3C accessibility guidelines, which by now are over five years old. As such, a number of these guidelines are outdated and don't apply anymore. In fact, some of them are now thought to hinder accessibility rather than help, so it's best to totally ignore these guidelines.
For example, an automated accessibility testing tool will probably insist that form items contain default place holding text. It may also insist that links need to be separated by non-link text. Neither of these guidelines are relevant anymore and their implementation could make accessibility worse rather than better.
Most guidelines aren't properly checked
Automated accessibility tools can check for a number of guidelines, and can tell you when a guideline isn't being adhered to. However, when the tool claims that a guideline is being fulfilled this may in fact be a false truth.
For example, if all images contain alt text then the software will report a pass for this guideline. But what if the alt text isn't descriptive of its image? What if alt text is crammed full of nonsensical keywords for search engines? How can an automated accessibility tool possibly know this?
Warnings may be misinterpreted
The reports generated by automated accessibility tools provide warnings, as well as errors. These warnings are basically guidelines that the automated tool can't check for, but which may be errors. Often they're not, and in fact they're often not even relevant. However, some people reading a report may try to get rid of these warning messages by making the appropriate changes to their site. By doing so, they may be implementing guidelines that needn't be implemented and inadvertently lowering the website's accessibility.
Conclusion
Automated accessibility testing tools can be useful as they can save a large amount of time in performing some very basic checks for accessibility. However, they must be used with caution and they cannot be used as a stand-alone guide for accessibility checking. Indeed, some expert accessibility knowledge should always be applied in evaluating a site accessibility, perhaps in conjunction with the fantastic web accessibility toolbar (http://www.nils.org.au/ais/web/resources/toolbar/) to help dramatically speed up manual checks.
About The Author
This article was written by Trenton Moss. He's crazy about web usability and accessibility - so crazy that he went and started his own web usability and accessibility consultancy ( Webcredible - http://www.webcredible.co.uk ) to help make the Internet a better place for everyone.