Table of Contents

Guided set up

This guide walks you through setting up a mod for Slay the Spire 2 from scratch. No prior experience with C# or Godot is assumed.

Note

Heads up! Setting up a proper development environment for any software can be time consuming and fickle, but you can do it!

Provided is a guide to getting started, from zero to a fully working (though pretty simple) mod. This document can be followed by people of many skill levels to getting to a stable environment where you can build their first mod.

If you already have a working knowledge of C# build systems or have already built a Slay the Spire 2 mod, you likely can get yourself set up simply through the manual instructions.

Install .NET 9

.NET is the platform that C# mods are compiled and run on. You'll need version 9.

  1. Download the .NET 9.0 SDK installer for your operating system from Microsoft. Note, you need the full SDK, not just the runtime.
  2. Run the installer

To verify it worked, open a terminal (on macOS: Terminal from Spotlight; on Windows: Command Prompt or PowerShell; on Linux: your terminal of choice) and run:

dotnet --version

You should see a version number starting with 9.. If you see an error, restart your terminal and try again.

Download MegaDot

MegaDot is a custom build of the Godot game engine that Slay the Spire 2 is built on. It is used to package your mod's resources.

  1. Go to https://megadot.megacrit.com/
  2. Download the version for your operating system

Install Visual Studio Code

Visual Studio Code (VSCode) is a free code editor that works great for C# development. You can use any other IDE, this is just my suggestion.

  1. Download and install VSCode from https://code.visualstudio.com/
  2. Open VSCode and go to the Extensions panel (the square icon on the left sidebar)
  3. Search for and install the C# extension (ms-dotnettools.csharp)

Install ModSmith

ModSmith is the modding framework your mod will depend on. It must be present in STS2's mods/ folder at build time.

Follow the instructions to install ModSmith.

Initializing your mod from the template

A Slay the Spire 2 mod needs a fair amount of "boilerplate" (glue code) to get working. A ModSmith mod for Slay the Spire 2 can be quickly generated using a dotnet template:

dotnet new install ModSmith.Templates
dotnet new modsmith-mod -o YourModName --StarterContent

Note that your mod's name must be one word. It is convention to use "PascalCase" for mod names.

Build and run your mod

Open a terminal inside your mod folder. Run:

dotnet publish

This compiles your mod, and copies the result to the game's mods folder. If the build succeeds, you'll see a message like Build succeeded.

Once the game is running with your mod, you can find some new content from the starter content. To quickly test, open the in-game developer console (using the ~ key) and type:

potion DROP_OF_GOLD

This will grant you an example potion which was included as part of your mod. Drink it, and you'll gain some gold.

If this didn't work, inspect the logs for your game by opening the developer console and running open logs.

Try making changes to DropOfGold.cs, and then recompile the mod:

dotnet publish

Restart the game, give yourself the potion again, and see if how your changes affected the potion!

Congrats! You are now a modder!

Next steps

Now that your mod builds and runs, explore the rest of this documentation:

  • Decompile Slay the Spire 2: Get access to all the Slay the Spire 2 source code and art assets for reference.
  • Concepts: understand the core systems (event hooks, localization, resource paths) in Slay the Spire 2.
  • Examples: browse working examples for custom cards, relics, events, and more.
  • API Reference: detailed documentation for every ModSmith class and method.

When you're ready to start adding your own content, remove the StarterContent from your mod, and start building!

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