Web accessibility evaluation tools can be very helpful;
however, they do not replace the need for human evaluation. Webster's
definition of "tool" as an "instrument used by a craftsman or laborer at
his work" is useful in understanding the role of automated web accessibility
evaluation tools.
Evaluating for accessibility requires knowledgeable human judgment.
No tool alone can determine if a site meets accessibility guidelines.
(However, a tool can determine if a site does not meet accessibility
guidelines.) Testing tools can increase the efficiency of evaluation.
Experience with assistive technologies is required to evaluate for
usable accessibility.
Consider using spell checkers to test for typing errors as an analogy
for accessibility evaluation tools. A spell checker can identify words
that are not in its dictionary, and it can suggest similar words to fix
the potentially misspelled word. A human must then decide if indeed the
word is misspelled (correctly spelled proper names might not be in a dictionary) and if
so, which is the correct spelling. Another issue is that spell checkers
will not identify wrong words that are properly spelled. For example, if
I type, "good text tool" when I meant to type, "good test
tool" the spell checker will not identify it as a spelling error.
Checking alternative text (alt text) for images is good example of using web accessibility evaluation tools to
increase efficiency, and of the requirement for human judgment. To meet
web accessibility standards and guidelines, all images must have equivalent alt
text. Images that convey no meaning, such as a transparent gif used as
a spacer, should have null or blank alt text.
Most all web accessibility evaluation tools help in checking for alt
text. For example, Bobby (www.cast.org/bobby) lists all images that are missing alt text.
However, no tool can tell if the alt text is
"equivalent" as required for accessibility. A designer could cheat
most tools by putting the same "dummy" alt text for all images.
Tools such as WAVE (www.temple.edu/inst_disabilities/piat/wave) further help a human evaluator judge if alt text
is appropriate. WAVE displays the alt text adjacent to the image so that you can see the image and the alt text together in the context of the page.
Web accessibility evaluation tools can save time and effort, but cannot replace knowledgeable human evaluators. Rather than thinking of tools as a substitute for human evaluation, think of tools as an aid to human evaluation.
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