To add mods to a Project Zomboid server, put each mod’s Workshop ID in WorkshopItems= and its mod ID in Mods= in servertest.ini, then restart the server. On start, the server downloads every listed Workshop item before loading the world, and players are asked to download the same items when they join. Leave either line empty for a mod and it downloads but never loads, with no error to tell you why. Here’s how to find both IDs, add map mods, and fix the errors modded servers run into.
How Project Zomboid server mods work
A Project Zomboid server tracks mods with two lists. WorkshopItems tells it what to download from the Steam Workshop. Mods tells it what to switch on. They use different IDs, and a mod has to be in both. Map mods need a third entry, the map’s folder name in Map=. Players never install anything by hand: when they join, the game lists the server’s Workshop items and downloads them.
| Line in servertest.ini | What goes in it | Example |
|---|---|---|
WorkshopItems= |
Numeric Workshop IDs, separated by semicolons | WorkshopItems=514427485;513111049 |
Mods= |
Mod IDs (text), separated by semicolons | Mods=ModOne;ModTwo |
Map= |
Map folder names, with Muldraugh, KY kept in the list |
Map=YourMapFolder;Muldraugh, KY |
Step 1: Find the Workshop ID and the mod ID
The Workshop ID is the number at the end of the mod’s Steam Workshop address, after ?id=. The mod ID is a short text name. Most mod pages list it at the bottom of the description as “Mod ID:”, and The Indie Stone uses the same “Workshop ID: … – Mod ID: …” format in its own posts. If the page doesn’t say, the mod ID is the id= line in the mod’s mod.info file.
- One Workshop item can hold several mods. RV Interior, for example, lists two mod IDs on its page. Add only the ones you want.
- The folder name isn’t always the mod ID. Copy the ID from the page or
mod.info, not from the folder. - Map mods also need their map folder name, the folder inside the mod’s
media/maps/. - Mod IDs can contain spaces and capitals. Copy them exactly.
Already downloaded the mod in your own game? Its files are in your Steam folder under steamapps/workshop/content/108600/<Workshop ID>/mods/, and each mod folder there has its mod.info.
Step 2: Add them to servertest.ini
Stop the server, then open Zomboid/Server/servertest.ini (or <server name>.ini if you start it with -servername). Add the IDs to the end of each line, separated by semicolons with no spaces between entries. Don’t use commas.
WorkshopItems=514427485;513111049
Mods=ModOne;ModTwo
Map=YourMapFolder;Muldraugh, KYThe two Workshop IDs are the example the game itself prints above that line in servertest.ini; swap in your own, along with your mod IDs and map folder. For maps, put the map folder in front of Muldraugh, KY and keep Muldraugh, KY in the list, which is what most map mods ask for. Some newer guides write mod IDs with a leading backslash, like Mods=\ModOne;\ModTwo. The 42.20 server strips backslashes before it reads the list, so both forms load the same.
Step 3: Restart and check the log
Start the server. Before it loads the world it signs in to Steam and downloads every item in WorkshopItems, so the first start after adding big mods takes longer. If a download fails, the server stops instead of starting without the mod. Open Zomboid/server-console.txt and read the last lines to see which item it was. Once it’s up, join from the game: you’ll get a list of the server’s Workshop items to download, then you’re in.
How to add mods to a hosted server
The steps above work on any machine you have file access to, your own or a rented one such as GameTeam’s Project Zomboid server hosting. Upload or edit servertest.ini with the server stopped and restart it. For a game started with the Host button, use Manage settings… on the Host screen instead. Its Workshop section lists “Workshop items used by this server” and lets you add installed items, or other items by ID, without editing files.
Can you add mods to an existing Project Zomboid server?
Yes. Add the IDs and restart, and the mods load into your current world. Back up first: copy Zomboid/Saves/Multiplayer/<server name> with the server stopped. Removing a mod from a world that already uses it is riskier than adding one, because anything that mod added to the world can vanish or throw errors. Remove mods one at a time and check the log after each restart.
Build 42 and mods
Build 42 changed a lot under the hood. When multiplayer arrived in 42.13 The Indie Stone told players to expect mods to need updating, and many Build 41 mods were never updated. Before you add a mod to a Build 42 server, check its Workshop page: most say in the title or tags which build they’re for (a “Build 41” tag or “[Only for B41]” in the title means it won’t work on 42). If your mods broke right after 42.20.4, update the server to 42.21. That patch re-enabled two Lua functions that 42.20.4 had switched off, which some mods rely on.
One more warning from the developer, posted in October 2026: The Indie Stone officially supports Lua mods only. Java mods change the game’s own code, usually need manual installation and a special loader, break with game updates, and can run any code they like on the machine. Stick to normal Workshop mods on a server unless you trust the author completely.
Keeping mods updated
When a mod author pushes an update, every player’s Steam downloads it, but the server keeps the copy it fetched at its last start. Players then can’t join and see “Workshop item version is different than the server’s”. The fix is a restart: the server downloads the current version of every Workshop item each time it starts. To check without restarting, run /checkModsNeedUpdate. The answer is written to the log and to chat. Many groups restart on a schedule for exactly this reason.
Troubleshooting Project Zomboid server mods
| Symptom | Likely cause | Fix |
|---|---|---|
| Mod not working on the server, nothing changes in game | The Workshop ID is in WorkshopItems but the mod ID is missing from Mods (or the reverse) |
Add the missing entry, restart |
| “Workshop item version is different than the server’s” | A mod updated after the server started | Restart the server |
| Mods not downloading when joining the server (“Error downloading workshop item”) | Steam couldn’t fetch the item on the player’s side | Restart Steam and rejoin; if one item always fails, check its Workshop page still exists |
| Kicked: “your game files do not match the server’s”, or “File doesn’t exist on the server” | The player has a mod enabled that the server doesn’t use, or changed game files | Turn off extra mods on the player’s side, verify game files in Steam |
| Server stops during start after adding a mod | A Workshop download failed, or the mod errors on load | Read the end of server-console.txt; remove the last mod you added |
| Mod loads but crashes the server or players | Built for the other build, or clashes with another mod | Check its build tag; test it alone on a copy of the world |
For the ports, files and other errors that aren’t about mods, see the Project Zomboid dedicated server guide. Every other line of servertest.ini is explained in Project Zomboid server settings explained.
The easy way: let the copilot install them
On Project Zomboid server hosting from GameTeam, you don’t touch either list. Tell the built-in AI copilot “add these three Workshop mods” with the links. It puts the Workshop IDs in WorkshopItems, the mod IDs in Mods and any map folder in Map, then restarts the server. When a mod update locks players out, ask “why can’t my friends join?” and it reads server-console.txt, finds the version mismatch and restarts the server for you. You pay per GB of RAM, from $0.49/GB a week, and a modded server costs the same per GB as a vanilla one.
FAQ
Do players need to install the mods themselves?
No. When they join, the game shows the server’s Workshop items and downloads them. They only need Steam running.
How do I add all the mods from a Workshop collection?
WorkshopItems takes the IDs of individual items. Open the collection, copy each item’s ID into WorkshopItems, and add each mod ID to Mods.
Why do my mods work in single player but not on the server?
Your own game enables mods from the Mods menu, but the server only loads what’s in its Mods= line. Copy the mod IDs over, along with the Workshop IDs.
Does the mod order matter?
Mostly when mods depend on each other or overlap. Put libraries and frameworks a mod requires before the mods that use them, and put map folders in front of Muldraugh, KY.
How much RAM does a modded server need?
More than vanilla. 4 GB suits a small unmodded group. A modded Project Zomboid server with a long mod list or a big map mod is safer on 8 GB.