Checkpoint64 has a preset for tModLoader: it already knows where the save folder is, backs it up automatically and keeps every version. Everything this site has on tModLoader:
tModLoader
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Save file location
Windows:
%USERPROFILE%\Documents\My Games\Terraria\tModLoader
macOS:~/Library/Application Support/Terraria/tModLoader
Linux:~/.local/share/Terraria/tModLoader -
Backup guide
Mods are the number-one cause of save corruption. Checkpoint64 keeps a full version history of your modded saves — modded Minecraft, Skyrim, Stardew and more — so a bad update or a removed mod is one rollback away. Free download.
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Sharing with friends
How to share your tModLoader world with friends, from playing live to taking turns when the host is offline.