I recently discovered the GraphViz::Regex Perl module for diagramming regular expressions:
I have added that functionality to my online regex tester at http://www.myregextester.com/
Simply check the box "DIAGRAM" before submitting your pattern in the tester.
Unlike the saved examples, diagrams are kept on a temporary basis only (currently removed daily). However, if you save an example with the "DIAGRAM" checkbox selected it will recreate the diagram when recalled.
The diagrams are returned in PNG format.
There are likely a number of unforseen issues with the module's interpretation of regex syntax, unfortunately I cannot change it's functionality so it is what it is. One known issue I would note is that it does not take modifiers into account when creating the diagrams.
I have also added "WORD LIST" function to the tester using the Regex::PreSuf Perl module:
It allows for the creation of a match pattern based on a list of words, pattern is somewhat optimized but in my testing the results varied (if you encounter optimization issues using this function, consider using the "OPTIMIZE" checkbox instead and enter a match pattern with the words in your word list separated by | character).
The "WORD LIST" tool can be found in the "TOOLS:" dropdown list at the site.