I want to see what words appear the most frequently in Ecclesiastes. Is there a tool to do that?
A Word List is an option
Or the Concordance Tool:
Not exactly frequency, but depending on your needs it may also be worth consulting the new Important Words guide section, which will show you the words that are discussed the most by commentators.
Adding to Graham's suggestion, you can also use Concordance with Hebrew lemmas (if those are the words you're looking for).
One advantage of Concordance is that you have many filters to narrow your focus.
+1 I absolutely love Concordance for this!