If you're trying to install a mod that comes as a .json file only — that's not possible. JSON is just config data, not the mod itself. You still need the .pbo files in @ModName\addons\.
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Suppose you downloaded hardcore_loot_types.json from a community forum. Open it in your text editor and quickly scan for: dayz json files install
Usually for custom keybinds or UI mods → put in Documents\DayZ\ or mod's local folder. If you're trying to install a mod that comes as a