The project is designed to display tags for recently listened tracks from Last.fm.
Enter your Last.fm username on the following page, and get a list of your recent tracks with their tags.
https://synthwaver.github.io/musmetaniac/recenttracks
Now it often happens that no tags are displayed for a track. There are problems with database synchronization on the Last.fm side, and the Last.fm API may return an empty list of tags for the track. Unfortunately they cannot say when this will be fixed. But you can always click the View on Last.fm link and check tags there.