Just because I find I always have to look up whether I called it "$needsKey" or "$needKey," whether it was a number or a Boolean, where it first got used...
Twine 2 current relies on each of the individual story formats (Harlowe, Snowman 2, SugarCube) to implement their own debugging features, all the Twine application does is ask the selected story format to turn debug mode on when you use the Test option.
This is why currently only Harlowe has a Debug View button.
SugarCube has its StoryInit passage which does this, as you should be defining all your variables there if using SugarCube. And you can format the passage with comments to remind you where everything goes.
Strikes me as one of those things where variable tracking should be the player's own responsibility though. However good something in Twine would be, it would never compare to an external design plan document.
In Twine 1.x, click on Story, Story Statistics to see a list of all variables, but no, it doesn't say how they are used in the story due to the fact that variables aren't initiated that way. Every variable can be of any valid type.
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This is why currently only Harlowe has a Debug View button.
Strikes me as one of those things where variable tracking should be the player's own responsibility though. However good something in Twine would be, it would never compare to an external design plan document.