At Silktide, we believe the right approach to accessibility is a blend of automated tests (to cover a large amount of your web estate quickly) and manual testing (which covers individual elements).
Why is this?
Automated testing is an excellent way to get a good understanding of WCAG issues across your site that can be unambiguously tested by a computer.
By that, we mean WCAG success criteria that do not require any interpretation of the outcome.
For example, WCAG mandates that each page contains a descriptive title, using two tests under section 2.4.2.
Ensure all pages have a page title
Check that each page has an appropriate title
Is this automatically testable? Well, partly, yes.
It’s possible to check a section of HTML and determine whether the title exists.
But it’s not possible to check whether the title is appropriate (i.e. describes the content of the page).
Computers are unable to understand the context (at least, for the moment). Until they do, workarounds are required.
Silktide will tell you if a title is present and alert you when it is not (which would be an unambiguous failure). If a title is present we’ll flag it as a ‘requires manual attention’ issue. You can then read the title, decide if it is appropriate for the page, and approve it.
This is just one example. WCAG contains hundreds of manual and automated checks.
If your website has scored 100% in the Index, then that means in our opinion and, according to all the unambiguous tests we perform against WCAG, you are making your site as accessible as it can be against these criteria.
Remember, the Index is based only on a selection of pages of your entire website. So a score of 100 only applies to those pages we have tested.
Automated tests, whichever platform you use, will cover perhaps 30-40% of WCAG. They are unlikely to cover the in-depth manual checking that an organization like GDS would carry out.
We always recommend you employ manual testing when implementing web accessibility.
We created an article with further information entitled How do I know when my website is accessible.