Mods

1. Subscribe on the Steam Workshop page for Project Zomboid. Steam downloads it.
2. In the game, open Mods from the main menu and switch it on. Mods marked for Build 42 only show up on Build 42.
3. When you start a new game, check the mods for that save: each save keeps its own mod list.
4. Adding mods to an existing save is usually fine; removing mods that add items or map changes can break it. Back up first.

A mod must say it supports Build 42. Build 41 mods generally do not work on Build 42, and Build 42 changed often during Unstable, so check the mod’s last update against the game version.

The full statements are on news.

Servers list Workshop items and mod IDs in their settings; players joining download them automatically. Every player must run the same mods and versions as the server. Full instructions, including the INI lines, are on hosting a server.

1. Disable all mods and test. If the game works, turn them back on in halves until it breaks.
2. Check the mod’s Workshop page for a Build 42 version and the date of its last update.
3. Look in the console log (console.txt in your Zomboid user folder) for the mod name near the error.
4. Unsubscribe from anything that has not been updated since the last major patch.

Every mod on your PC lives in one of two places. Workshop subscriptions download to Steam\steamapps\workshop\content\108600\<Workshop ID>, one numbered folder per item. Anything you install by hand, or write yourself, goes in the Zomboid user folder: C:\Users\<you>\Zomboid\mods on Windows and ~/Zomboid/mods on Linux and macOS. That same user folder holds your saves, the Server folder with your hosted-game settings, and the console.txt log that the troubleshooting steps above rely on.

Two different numbers identify a mod, and mixing them up is the most common reason a server refuses to load its mod list.

Load order matters less than guides suggest. The game only cares when two mods ship a file at the same relative path, for instance under media/lua or media/scripts, and the one loaded later overwrites the other. Map mods that edit the same cells cannot be fixed by reordering at all. Our pick: let the game write the lines for you. Set the mods up in the Host menu's Manage Settings screen, then copy the generated WorkshopItems= and Mods= lines into a dedicated server rather than typing IDs by hand.

The quickest way to understand how mods are built is to make one that does almost nothing. Build 42 changed the folder layout: a mod needs a common folder or a version folder to be recognised at all, and most authors use both. In your Zomboid\mods folder create this tree.

1. MyFirstMod\common\ may be left empty. Files here load for every build.
2. MyFirstMod\42\mod.info is a plain text file with at least name=My First Mod and id=MyFirstMod_KnoxTools. Pick a long, distinctive id; it must be unique across every mod on Steam, and short ids collide. Optional lines are description=, poster=poster.png and require=.
3. MyFirstMod\42\media\lua\client\MyFirstMod_Hello.lua holds the code. Client Lua runs on each player's machine, server Lua runs on the server, and shared Lua runs on both.

Inside the Lua file, register a function on a game event, for example Events.OnGameStart.Add(function() print("MyFirstMod loaded") end). The game loads every .lua file in those folders automatically, with no registration step, and print() output lands in console.txt. Start the game, open the Mods menu, enable My First Mod, load a save, then check the log for your line.

When a mod has both common and a version folder, the game loads common first and then the version folder closest to the build it is running, and files in the version folder override files at the same path in common. A folder named 42 counts as 42.0. Keep the first mod Lua-only: it stays inside the sandbox The Indie Stone supports, and it is exactly the kind of mod the security checklist above is happy with.

Project Zomboid updates arrive through Steam branches, and the branch you are on decides which mods work and which saves open. Right-click the game in your library, choose Properties, then Game Versions & Betas (older Steam clients call it Betas). The names are case-sensitive.

Rolling back is the same menu in reverse: pick the older branch, let Steam download it, and launch. Two things cannot be rolled back. A world opened on 42.22 may not load again on 42.21, and a Build 42 save never opens on legacy41, so copy the whole Zomboid\Saves folder before switching in either direction. Client and server versions must also match exactly, so a 42.21 client cannot join a 42.22 server.

What breaks on a patch is fairly predictable. The 42.22 notes single out mods that touch tiles, maps or crafting, and move tile definitions into a tile_definitions subfolder under media, so map and tile mods are the first to need updates. Your Workshop subscriptions survive a branch change, which is the trap: Build 41-only mods left enabled on Build 42, or the reverse, are a common cause of "unexpected error" crashes. Our pick is a separate Workshop collection per branch, and a look at each mod's last-updated date before loading a save after any update. See version history for what each patch changed.