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(Example: Slugcat Camo Mod by LodeRunner + Co-op Mod by OriginalSINe, both running through this mod loader. Check out for more released mods, which may some day be made compatible with this loader.)


Proof of concept Rainworld Mod Loader, almost at a state of being useful.

If you are a mod developer, please do get in touch and provide feedback! I'm on the Rainworld Discord in #modding.

(This same approach could be used to create mod loaders for any Unity game, really.)

Developing Mods

  1. Download this repository

  2. If your current Assembly-CSharp.dll file is already modded, the injector will not detect this and probably fail. Make sure you have the vanilla version of the game installed.

  3. Paths to important game folders are currently still hardcoded into the code and project setup. They will be different on your machine, so make sure to change the following:

  • RainWorldInject.csproj -> Build/OutputPath, should be set to Rain World\Mods
  • ModLoader.csproj -> Build/OutputPath, should be set to Rain World\RainWorld_Data\Managed
  • MyCustomMod.csproj -> Build/OutputPath, should be set to Rain World\Mods\MyCustomMod (do this for any mod project in the solution)
  • Similarly, references to Assembly-CSharp.dll and UnityEngine.dll need to be pointed to files in your Rain World\RainWorld_Data\Managed folder.

You should now have a VS2017 solution that patches your game when ran, builds the mod assemblies and puts them in the game mod folder. Do that once, and you should be able to launch the game and see the mods take effect. This can be verified in the produced consoleLog.txt file. If anything goes wrong, check exceptionLog.txt.

Note: currently this project contains multiple example mods which will eventually migrate to their own repositories. They're purely there to help quickly iterate on the mod api design. You can delete them, overwrite them, or enable/disable them in the solution's build configuration.

  1. Optionally, copy lib\PatchedMono\mono.dll from this repository to Rain World\RainWorld_Data\Mono, after backing up the original you find there. This will let dnSpy's debugger attach to the game.


For debugging I still recommend using dnSpy. If you load the game's assembly in there, and manually add your installed mod assemblies, and then launch the game through dnSpy's debug menu, its debugger works like a charm.

I've tried getting VS2017's debugging tools to work with the game, but haven't managed it yet. And besides, dnSpy's decompiled code is nicer to read.

The mod loader also automatically enables logging to consoleLog.txt and exceptionLog.txt, so all your Debug.Log, Debug.LogWarning and Debug.LogError calls ends up there.

Note: There is a caveat to using a debugger due to Harmony, see Known Issues.


The existing approach to modding Rainworld is to load the game's dotnet assembly using a tool called dnSpy, which lets you see decompiled source. You then have to edit the low level IL assembly code to do anything, deal with all sorts of cryptic errors, and after that your code is stuffed into the game DLL.

This workflow is not great for writing and maintaining comprehensive modifications.

How Does It Work?

An injector program takes the vanilla game dll and injects a small mod loader routine. This only has to be done once to enable mod loading for an installed version of the game.

The mod loader will then load custom DLLs with mod-only code when the game starts up, and get the game to call into it.

The loader looks for mod assemblies in the Rainworld/Mods folder. Anything called ******Mod.dll that contains an implementation of the modding interface gets loaded. Any static class that has a static void Initialize() and a name that ends with ******Mod will have that method called.

The Harmony framework is currently used to inject your mod hooks into the game's code. Check out the provided example mod projects to see how it's done.

Important: the exact way the mods are hooked into the game's many functions is still subject to change.

Three big wins:

  • The game can load multiple mods at once. (Providing they don't conflict, which requires some developer care. The modding API can't guarantee that any two mods go well together, but their developers can.)
  • You can write your code in visual studio, in C#, organize it into separate DLLs, have dependencies, use source control, and so on.
  • Mods and modding APIs don't need to redistribute copyrighted code in Assembly-CSharp, but can be locally applied as a patch to your game install with an easy to use patching program. The Hollow Knight modding community has encountered and discussed this issue, leading to a similar approach.

Known Issues & Todo

  • As soon as Harmony is used to patch the game's assembly at runtime, dnSpy's debugger can no longer respond to break points set in any patched methods. This is counterproductive, and a serious argument in favour of offline patching instead of runtime patching.
  • Having no mod API whatsoever and relying entirely on Harmony for creating your mod is not great. Should identify some common modding patterns (e.g. adding a new creature) and create easy to use infrastructure for this.