Build 42 Mods Guide — B42 Compatibility, Best Workshop Mods & Installation

No — Build 41 mods do not carry over to Build 42, and this is the single biggest gotcha of the whole update. Build 42 rebuilt the modding framework (items, crafting, map, UI and server systems all changed), so a Workshop list that worked on B41 silently breaks or crashes on 42.20. The good news: most major B41 mods have been re-released for B42, and there is now a big, actively maintained B42 mod scene. This guide covers how to tell what works on 42.20.4, recent breaking changes, the best current picks, and installation on both single-player and dedicated servers.

Why B41 mods break (and how to check compatibility)

The B42 framework changes mean compatibility is not assumed — it has to be declared. On every Workshop page look for these four signals:

1. Explicit B42 mention — title/description referencing "B42," "Build 42," or a specific version (e.g. "42.14"). The Steam "B42 compatible" tag helps but is not proof.
2. Recent update date — B42 patches land every few weeks and routinely break mods; a mod updated within the last month is far safer than a 2024 one.
3. Comments/works — player reports of "works on 42.20" or crash complaints in the comments are the ground truth.
4. Author status — "B42 support planned" is a no; "B42 version released" is a yes.

Red flags to avoid: last update before December 2024 (when B42 unstable launched), description only mentioning Build 41, and comment sections full of "crashes on B42."

Best Build 42 mods (community-vetted, 2026)

These are the frequently recommended, actively maintained picks that appear across current B42 round-ups (WinterNode, Supercraft, linuxbuz, FinalBoss — all checked July 2026). Always re-verify on the Workshop before subscribing.

Most gameplay mods need to be installed on both client and server for multiplayer. Share your list as a Steam Workshop collection so the whole group subscribes in one click — mismatched client/server mod lists are the #1 cause of "can't connect" complaints (the error fixes page diagnoses that exact symptom).

Installing mods — single-player

1. Subscribe to the mod on the Steam Workshop (it downloads automatically into the game).
2. Launch the game, go to Mods in the main menu.
3. Enable the mod (toggle to on) — and check Required items for any dependencies to enable too.
4. Load your save. Enabling a mod mid-save is usually fine on B42; disabling a mod that the save depends on is what breaks things — the save's mods.txt still lists it.

Installing mods — dedicated server

On a server, mods go in servertest.ini as two parallel lines:

WorkshopItems=<numeric-workshop-id-1>;<numeric-workshop-id-2>
Mods=<ModID1>\<ModID2>

• Workshop ID = the id= number in the Workshop URL.
• Mod ID = the identifier the author declares (shown on the Workshop page).
• B42 format change: every Mod ID needs a trailing backslash (Mods=BRITA_ARMOR_PACK\), unlike B41.
• Restart the server to download and load them. Connecting clients are auto-offered the server's subscriptions at handshake.

Full walkthrough plus RAM implications of heavy mods in the dedicated server guide.

Common mod mistakes (and how to avoid them)

1. Running B41-only mods on B42 — silent bugs that get blamed on the game. Apply the compatibility table above before subscribing.
2. Mismatched client/server subscriptions — symptom: "I can't connect." Fix: shared Workshop collection.
3. Auto-updates breaking mods mid-patch — B42 updates every 2–4 weeks and breaks 1–3 mods each time. Pin Workshop versions on dedicated servers until you've verified the new patch.
4. Stacking too many heavy mods — a 30+ mod list costs RAM (see the server table in dedicated server) and makes diagnosing crashes miserable. Fewer, stable mods beat a large broken collection.

42.20.2 hotfix: the percent-sign (%%) rule and .json support

The 42.20.1 and 42.20.2 stable hotfixes (August 5, 2026) introduced two notable modding API updates:

• Percent-sign escaping: Mod authors must now write %% in their files to show a % in game (e.g. a mod tooltip saying "50% less" must use 50%% internally). A temporary workaround still accepts the old bare %, but the workaround will be removed in a future unstable update — mods that aren't updated will misprint percent signs once it's gone.
• Error logs highlight exact file locations so mod makers can easily locate unescaped % instances.
• JSON support: Mods gained the native ability to write .json files for easier data storage and configuration.

42.20.4 hotfix: loadstring / loadstream removal & mod breaking changes

The 42.20.4 stable hotfix (August 26, 2026) shipped a major security overhaul that directly impacts certain mods:

• What changed: The Indie Stone permanently removed the loadstring and loadstream methods from the game's Lua sandbox to close remote execution vulnerabilities.
• Which mods are affected: Any mod that relied on dynamic code evaluation, encrypted payload decompression, or server-to-client code injection. This includes older versions of UI mods (such as older CleanUI releases) and custom server-side anti-cheat tools.
• Symptoms: If an affected mod is active, the game or server console will throw a Lua error: attempt to call global 'loadstring' (a nil value).
• How to fix:
  1. Check the mod's Steam Workshop comments for a 42.20.4 update notice or author patch.
  2. Disable the offending mod until the author migrates to the official command handler.
  3. Mod authors must create native methods and trigger them via standard client/server command payloads instead of dynamic string evaluation.

Verified on 42.20.4 · Last checked 2026-09-05

B41-incompatibility statement from The Indie Stone's B42 announcements and consistent hosting-provider documentation; compatibility signals and mod shortlist from current B42 round-ups; B42 Mod ID backslash format from hosting-provider mod install guides; percent-sign rule from the official 42.20.2 stable release notes; loadstring/loadstream security deprecation verified from the official 42.20.4 stable hotfix announcement (August 26, 2026). Workshop compatibility changes constantly — re-check each page before subscribing.