I am not very well familiar with details in how free licences work and interact, so I'm seeking help.
Situation in brief: There is a desktop application X licensed under AGPL v.3. Users of X may install an X's browser extension (also under AGPL v.3) which imports parsed data from common web-sites to X's desktop app (for that, the desktop app runs a server that accepts data from the browser's extension).
Now, I've developed a small app, Y, and I want it to be able to import data from the X's browser extension. For that, I only need to know the format of the data sent by the X's extension, and to mimic the X's server in my app Y. I do not use the X's source codes for developing the server at all, I build it from scratch and make it correctly accepting the data from X's browser extension.
May such situation raise any licence/legal issues? Will that depend on the licence I will choose for my app Y?
Edit: I do know the format of the data sent by X's extension - it is simple JSON data. It is documented at X's website, although not in very detail. Details are easily found by direct inspection of the JSON object. But I should add that this documentation is aimed at contributors who wish to improve/add webpage-parsing capabilities of the X's application itself rather than other apps (although there is no explicit statement that this information cannot be used for importing data into other apps).
If that helps, the application X is Zotero.