Backup

World Downloader automatically creates a backup of the downloaded copy of a world as soon as it stops downloading. You can configure the way this works using the backup GUI.

By default, when you stop downloading and saving is finished, the entire world is backed up as a zip folder, located in the saves folder. You can also have it copy the world folder completely, or just not make a backup.

Note that zip backups are not playable in-game, while world folder backups are playable in game (but if you play in it, the backup is no longer as it was). You can manually unzip the zip backup if you want to play it in-game.

Beware that each backup is a full backup - neither are incremental backups. As the world gets larger, your backups will get larger as well. This is exacerbated if you have multiple dimensions in the same world - saving each dimension creates a full backup. This can be avoided by creating separate multiworld worlds for each dimension.

If you do disable automatic backups, remember that you can manually create a backup by opening the world folder (located in %appdata%\.minecraft\saves) and manually zipping the world. You can also clear out old backups there if you want.