Looks great, and it works great on my desktop. I also quite like its simplicity.

However, after playing around with it for a bit, I noticed one glaring flaw. It stores its playlists in one (potentially) huge playlists.json file. It's great if you're manually creating playlists from scratch. However, I've had several playlists that I've compiled from my time in iTunes, and then Media‌Monkey, all of which are now in an m3u format. I can play them in Harmonoid just fine, though it only shows song info for the first song in the playlist, even though does play the rest of the songs just fine.

Meanwhile, since Harmonoid also has a mobile version, I also played around with it. My playlists worked better over there as it shows the track information for all tracks, not just the first one. I haven't dug up the files to see how they're being stored, though.

I guess a feature like "playlist import/export" can be requested. Personally though, looking at the JSON data within the playlist.json file, however, IDK:

{
    "playlists": [
        {
            "name": "History",
            "id": -2,
            "tracks": [
                {
                    "uri": "file:///home/user/Music/ArtistName/AlbumName/TrackNumberAndTrackName.mp3",
                    "trackName": "TrackName",
                    "albumName": "AlbumName",
                    "trackNumber": 1,
                    "discNumber": 1,
                    "albumLength": 1,
                    "albumArtistName": "AlbumArtistName",
                    "trackArtistNames": [
                        "TrackArtistNames"
                    ],
                    "genres": [
                        "Genre"
                    ],
                    "timeAdded": 1554270035,
                    "duration": 0,
                    "bitrate": 0
                },
                // More tracks…
            ]
        },
        {
            "name": "Liked Songs",
            "id": -1,
            "tracks": []
        }
    ]
}