I'm all for people looking things up for themselves BUT did you actually do the search you suggested before posting your comment? Because for giggles I decided to do as you suggested to them and didn't see a link to the said tool in the first 3 pages returned by said search engine, at that point I got bored and stopped looking.And as for where it could be found, I hear there's something called GOOGLE, a search engine. :noexpression:
The game is made using Twine 2 and the SugarCube 2 story format, and that engine has a built-in debugging object named SugarCube which can be used within your web-browser's Developer Console to access the internals of the game. In SugarCube 2.x the variable values of the current moment in History can be accessed via the SugarCube.State.variables collection, and changes to the properties stored in that collection will effect the next Passage shown.