What is RimWorld Mod MCP?
RimWorld Mod MCP, by the GitHub user mushroomTW, gives Claude Code, Codex and other MCP clients the parts of RimWorld modding a coding agent cannot do alone. It indexes the game's Def XML and C# symbols, decompiles the game and installed mods on demand, creates and builds mods with structured compiler errors, and launches RimWorld in an isolated session whose errors and game state flow back to the agent through a small in-game bridge mod.
It targets RimWorld 1.7 only and ships as a single self-contained executable for Windows, macOS and Linux. The repository was created on 26 September 2026, released v0.3.1 on 25 October 2026, and has 3 stars and no forks under the MIT licence. It never publishes to the Steam Workshop and, apart from one NuGet reference package on the first build, makes no network calls.
How to install RimWorld Mod MCP
Download the release executable and register it with the argument stdioIs RimWorld Mod MCP worth it?
Most game-modding servers stop at search. This one closes the loop: an agent can look up how a Def or class works, write the mod, build it, launch the game with only that mod enabled and read back what broke. Build failures come back as error code, file, line and column instead of raw MSBuild output, and the bridge reports whether a map has loaded, the tick, whether the game is paused and which dialogs are open, so the agent can wait for a playable state before judging a test.
The indexing is layered sensibly. Reading IL metadata directly builds an index of roughly a hundred thousand symbols in seconds, with full inheritance chains; single members decompile on demand in milliseconds; full-text search over decompiled source fills in over minutes in the background. find_def_usages traces a Def across XML cross-references and C# DefOf fields, which is the check modders need before writing translation files. Other mods' assemblies can be decompiled and searched too, which helps with compatibility patches.
Isolation is thought through. Test sessions point RimWorld at a temporary save folder, generate a ModsConfig.xml with only the mod under test and its dependencies, link the workspace into the Mods folder, refuse to start while the game is already running, and remove the links without touching the mod source. The bridge connects only to 127.0.0.1 on port 49460 with a single-use token per session. The weak spot is writes: create_mod, build_mod and run_test_cycle accept any local path, with no allow-list, so the client's permission prompts are the only boundary.
The README compares it fairly with four rivals. Modmixer is a desktop app with its own agent and Workshop publishing; RimSage and RiMCP_hybrid only research; RimBridgeServer gives deeper control of a running game, with screenshots and UI actions, and the README calls it complementary. The real risk is maturity: eight releases in its first month, one maintainer, commit messages largely in Traditional Chinese, and RimWorld 1.6 explicitly unsupported. For a modder already on 1.7 with Claude Code or Codex, it is worth a trial on a side project.
Where it earns its place
A hobbyist modder maintaining a small RimWorld content mod
Port an XML and C# mod to RimWorld 1.7
Let the agent read the changed symbols with read_symbol, update the code, run build_mod until the diagnostics are clean, then run_test_cycle and poll list_test_diagnostics for errors. Free apart from model tokens; keep the mod in Git.
A modder writing a compatibility patch for a popular mod
Find which classes the other mod patches before adding a Harmony patch
Use inspect_installed_mod to decompile the other mod's assemblies, then search_source for the patched methods. The first decompile of a large mod can take minutes, but it runs per mod without blocking others.
A translator adding a language to an existing mod
Check every translatable field before writing Languages XML
Run find_def_usages on each Def to list XML and C# references, then write the Languages files and run build_mod to validate the XML. It avoids guessing which labels the game actually reads.
Before you commit
- Setup
- Download the executable for your platform from the latest release, mark it executable on macOS or Linux, register it with the argument stdio in your MCP client, call rimworld_status, then rebuild_index once. .NET SDK 10 is needed for building C# mods and the bridge.
- Integrations
- 19 tools across research, installed mods, build and testing. Examples are provided for Claude Code and Codex; any stdio MCP client works. Mod projects reference the RimWorld API through the Krafs.Rimworld.Ref NuGet package.
- Data and privacy
- Local only: game files, decompiled output, indexes and diagnostics stay on your machine, and the bridge connects only to 127.0.0.1 with a single-use token. Whatever the tools return still goes to your model provider. File-writing tools have no path allow-list.
- Limits
- RimWorld 1.7 only. Full-text source search is not ready until background indexing finishes. No screenshots or in-game interaction beyond diagnostics and coarse state. Starting a test is refused while the game is already running.
What’s good
- Research, build and isolated test in one local server
- Symbol index of about 100,000 symbols in seconds
- Structured compiler diagnostics and live game state
- No network calls and no Workshop publishing
What’s not
- RimWorld 1.7 only; 1.6 not supported
- No path allow-list on file-writing tools
- 3 stars and a single maintainer
- macOS build is not notarised
Best for
RimWorld 1.7 modders who already use Claude Code or Codex and want the agent to build and test its own changes.
RimWorld Mod MCP alternatives
RimWorld Mod MCP: common questions
- Is RimWorld Mod MCP worth it?
- A carefully designed modding loop for RimWorld 1.7 that does the research, build and test steps an agent cannot, from a six-week-old project with almost no users yet. We rate it 3.6 out of 5.
- How much does RimWorld Mod MCP cost?
- Free and open source (MIT). Needs a legitimately installed copy of RimWorld 1.7 and, for building, the free .NET SDK 10.
- What are the downsides of RimWorld Mod MCP?
- RimWorld 1.7 only; 1.6 not supported; no path allow-list on file-writing tools; 3 stars and a single maintainer; macOS build is not notarised.
- Who is RimWorld Mod MCP best for?
- RimWorld 1.7 modders who already use Claude Code or Codex and want the agent to build and test its own changes.
- Is RimWorld Mod MCP safe for company data?
- Local only: game files, decompiled output, indexes and diagnostics stay on your machine, and the bridge connects only to 127.0.0.1 with a single-use token. Whatever the tools return still goes to your model provider. File-writing tools have no path allow-list.
- What are the best RimWorld Mod MCP alternatives?
- The closest alternatives we have reviewed are Godot MCP.
Answers checked Nov 7, 2026.