Thanks for using this tool and for your comments.
Surely CSV and JSON are plain text. ;) I would like to say about file extensions, but I am not a native English speaker and do not have a good representation. I would be glad if you could tell me how to write it, if you could.
I have made a minimum simple level editor so that it is suitable for first time use by students in my game-making class. So this tool can only output TXT files for now (as foolproof). However, I plan to add the option to output other formats in the near future after I come up with a way for my students not to mishandle it.