Hey there, you made a great tool!
I just wanted to point out that the player was broken for me. I did some troubleshooting and found the problem. The player wouldn't load any json files and instead do nothing or other mysterious stuff.
The reason for that was that when a new json config file gets created, there are some json fields that have no items in them and I think that's why the player is not accepting the file.
I had to first add at least one dummy item into each empty json field. Then I could select the json file in the player and everything was working.
I thought you want to know that because I can imagine that this might happen to other people as well.
Cheers!