Your server installs Steam Workshop mods itself — you declare what you want in two config keys, restart, and the server downloads and loads them. Here's the reliable way to do it on Build 42, and how to back out when a mod misbehaves.
The two keys
In your server's config (Settings tab → the mods section, or the raw servertest.ini in the Files tab):
WorkshopItems=2857548524;2200148440
Mods=tsarslib;ExampleMod
- WorkshopItems — the numeric Workshop IDs, from each mod's Steam URL. This is the download list.
- Mods — the short Mod IDs. This is the enable list.
- Both are semicolon-separated. Commas break the list silently.
One Workshop item can contain several Mod IDs (a mod plus its library, or B41 and B42 variants side by side). The Mod ID is stated in the item's Workshop description ("Mod ID: …") — when a mod lists separate B41/B42 IDs, use the B42 one.
The rules that prevent 90% of mod pain
- B42-tagged mods only. Build 41 mods do not work on your Build 42 server — this is the single most common cause of "mods won't load". Check the Workshop page before adding.
- Dependencies first, in both lists. Library mods (tsarslib is the famous one) go before the mods that need them.
- One change set at a time. Add a batch, restart, verify, then add more — so a breakage points at its cause.
- Back up first. Take a manual backup from the Backups tab before every mod-list change; mods write into your world save. See Backups & Saves.
Applying the change
Mod changes apply on a restart — the server downloads new Workshop items during boot, so a restart after a big list change takes longer than usual. Watch the console: each mod logs as it initialises, and a red wall of Lua errors naming a mod means it loaded before its dependency (reorder) or isn't B42-compatible (remove).
When a mod breaks the server
If the server won't reach SERVER STARTED after a mod change:
- Stop the server.
- Remove the most recently added mod from both keys (or restore the config from your pre-change backup).
- Start again. If it boots clean, the removed mod (or its position in the order) was the problem.
Your world save is not harmed by a failed boot — the danger to saves is removing a heavily-integrated mod from a long-running world, which can strand its objects. That's what the pre-change backup is for.
Players and mods
Joining players auto-download the server's mod list — they don't add anything manually. If one player errors on join after a mod change while others are fine, their Workshop copy is stale: they unsubscribe the mod, verify files, and rejoin. More join fixes: Players Can't Join.
Need a hand?
Open a ticket with the mod's Workshop link and what the console showed — we're happy to sanity-check a mod list or dig out a Mod ID that isn't where it should be.