Virtual Hosting.com has drawn up a list of 25 Free Website Checkers, with a brief description of what each one does. The checkers are split into handy sections - General, Disability, and Usability - but automated checkers will only check the easy bits - e.g. colour contrast, HTML (HyperText Markup Language) and CSS (Cascading Style Sheet) code, etc - i.e. the bits for which an algorithm can be written.
However, whilst a website checker can check that alt text, for example, is used with an image and will tell you if it’s missing, it can’t actually tell you whether what that alt text actually makes sense. For example, alt text of “an image” or “asdfg” is not going be very useful to someone who doesn’t download images or for someone who uses tooltips to find out the relevance of the image (particularly where a description or title hasn’t been provided). So developers and content authors need a hefty dose of common sense to make sure that the aspects of a website that can’t automatically be checked by a computer are actually usable and accessible.
It’s often quoted (but I can’t remember by whom) that one could implement the whole of WCAG (Web Content Accessibility Guidelines) and still end up with an inaccessible site. Whilst an automated checker might find that the site is accessible based on a simple checklist, a human may find it unusable. Human involvement in checking accessibility is still necessary and as well as common sense, an understanding of accessibility issues and context is also required. For example, whilst a photo of Winston Churchill might have the alt text of “Photo of Winston Churchill”, if the photo is illustrating a particular point, it could be more relevant to say “Photo of Winston Churchill smoking a cigar” or “Photo of Winston Churchill in London in 1949″, depending on context.
So whilst automated web accessibility checkers have their uses, it’s important to remember that they generally don’t include an algorithm for common sense!