Data File Format API
 

Just a question, and one I'm pretty sure I know the answer to, but are the Army Builder Data Files' format proprietary?

Is there a public API or library that someone could use to create their own Army Builder plugins and/or accessories?

I'm guessing one would have to speak directly with Lone Wolf in order to license the usage of their format if it was proprietary, correct?

You've read the authoring kit manual? Near the bottom of the page is a topic called "Writing Custom Extensions". It describes (in very general terms) the sort of thing that could be written to output stat cards for a game system, for example.