Project Zomboid Server Mods (Build 42): WorkshopItems vs Mods, the Backslash Question, and Mismatch Fixes

Open your server's INI file (the default is servertest.ini; a renamed server uses its own name) and find two lines:

A worked example with two verified quality-of-life mods:

WorkshopItems=2313387159;2847184718

Mods=BetterSortCC;ProximityInventory

That is Better Sorting and Proximity Inventory: the first line fetches them, the second line switches them on. The two classic failure modes are mirror images. A Workshop ID with no matching Mod ID downloads happily and never loads. A Mod ID with no matching Workshop ID has nothing to load from. One Workshop item can also contain several separate mods; when it does, each Mod ID you want active gets its own entry in the Mods= line, while the Workshop ID appears once.

The Workshop ID is the number in the item's page address, and most descriptions repeat it at the bottom as "Workshop ID:". The Mod ID is the mod's internal name: most descriptions print it as "Mod ID:", and it is also the id= line inside the mod's mod.info file once downloaded. The two are never interchangeable. A mod's display title is a third thing entirely and belongs in neither line; "that DAMN Library" loads as a framework entry, not by its title. If a mod silently fails to load, a typo in the Mods= line is the first suspect: the server detects what it can, and the server logs (server-console.txt and the latest DebugLog) show which Mod IDs were actually found.

If you have read older server guides, you have seen the Mods= line written with a backslash before every entry:

Mods=\BetterSortCC;\ProximityInventory

That form was real: during the earlier Build 42 period, dedicated servers expected the backslash prefix, and several hosting guides written then still print it, a couple insisting it remains required. Current documentation for the stable builds writes plain IDs instead: the pz-fans server settings and mismatch guides for B42.19, the community wiki's server pages, and several hosts' current worked examples all use the unadorned form, and Pine Hosting states outright that current Build 42 versions no longer require the leading backslash that earlier Build 42 multiplayer versions used. So: on 42.19 to 42.21, write plain IDs. If your rented panel or an old backup produced the backslash form and the mods load, leave a working server alone; if mods silently do not load on a fresh setup, normalise the line to plain IDs and check for typos before you change anything else. One route skips the question entirely: a server set up through the in-game Host menu has a Steam Workshop panel in its settings that writes both lines for you when you install mods there.

Two rules apply to both. The server downloads its WorkshopItems at startup, so a restart is part of every mod change. And the client-side Mods menu does not synchronise a dedicated server's INI: what a joining player's game enables locally is separate from what the server demands, which is why the join flow checks the list item by item.

Map mods add one more requirement on top of the two lines: the map's folder name also goes into the Map= line of the server settings, placed before "Muldraugh, KY" and separated by a semicolon, so the server loads the new area ahead of the vanilla map. And like single player, a map belongs in the list before the world starts; adding one to a world that already exists is not supported.

New servers do better with a short, boring list that every client can run: interface and quality-of-life mods first (Better Sorting, Proximity Inventory, Map Legend UI), one immersion mod the group agrees on, and vehicles only with their framework library ahead of them in the order, libraries before the mods that depend on them. Our best Build 42 mods list has the verified candidates with their IDs; grow from there in small steps, restarting and testing after each addition.

The error reads "Workshop item version is different than the server's", and it means exactly one thing: for at least one Workshop item, the client's downloaded copy and the server's downloaded copy are different builds. It is a per-item staleness problem, not a wrong-edition error and not a sign the mod is broken. The join flow's Server Workshop Items screen tells you which item and which side to suspect:

Fix order, lowest risk first:

1. Match game builds. Client and server must be on the same game build and Steam branch; no cache trick fixes a branch mismatch.

2. Client side: fully restart Steam so a pending Workshop update completes, then rejoin.

3. Server side: stop the server cleanly and restart it. Host and dedicated servers fetch their WorkshopItems at startup, and an always-on server that never restarts after an author updates a mod is the single most common cause of this exact message: every updated client then fails against the server's old copy.

4. Compare the lists. The server's WorkshopItems and Mods should match what clients are expected to run, dependencies included.

5. One stubborn ID only: with the game and server stopped, delete that single item's folder under steamapps/workshop/content/108600/ and let it download again.

6. Last resort: delete the whole 108600 content folder and appworkshop_108600.acf, which forces a re-download of every Project Zomboid mod on that machine. Back up first, and expect every server you play on to re-fetch its full list.

Workshop authors update their mods on their own schedule, and the mismatch mechanics above mean timing matters. Practical server hygiene:

Joining walks them through it: the Server Workshop Items screen lists what the server requires and its state for their account, and items can be installed from there. They still need the matching mods enabled, and the server's list is the authority on what that is.

Yes for most mods: add both lines, restart, and play. Content that spawns in the world appears in areas the world has not generated yet, the same unvisited-cells rule as single player. Map mods are the exception and belong in a fresh world.

Work the short list: is its Workshop ID in WorkshopItems, is its exact Mod ID in Mods, is any framework it needs listed ahead of it, and did the server restart after the edit? One of those four is behind nearly every case.

In the Server folder inside the Zomboid user folder of the account running the server: C:\Users\<name>\Zomboid\Server\ on Windows, ~/Zomboid/Server/ on Linux and macOS. A server created under a different name uses that name's INI and companion files instead. Edit the files on the machine that actually runs the server.