Slay the Spire 2 Modding Tutorial

Version-aware documentation for building local C# and Godot content mods for Slay the Spire 2 Early Access.

Published version: GitHub Pages

Coverage

• current game layout, loader behavior, and version checks
• net9.0 projects referencing the assemblies shipped with the game
• the external mod manifest, dependencies, staging, and installation
• decompiling sts2.dll and inspecting SlayTheSpire2.pck
• [ModInitializer], semantic hooks, and Harmony patches
• model discovery, pools, unlock visibility, and localization
• detailed custom card, potion, relic, act event, and GUI examples
• Godot .pck resources and native UI integration
• logs, save-state troubleshooting, packaging, and release verification

Verified Baseline

• STS2: v0.103.3
• game commit: 460a0ece
• release metadata date: 2026-05-29T13:36:05-07:00
• target framework: net9.0
• bundled .NET runtime: 9.0.7
• main PCK format: Godot 4.5.1

Early Access updates can change signatures and loader contracts. Re-check release_info.json, sts2.runtimeconfig.json, and sts2.dll before maintaining a released mod.

Reading Order

1. Environment setup
2. Game layout and loader surface
3. Project structure, build, and manifest
4. Reverse-engineering workflow
5. Entry points, Harmony, and hooks
6. Content infrastructure, assets, and localization
7. Native UI and runtime inspection
8. Debugging and iteration
9. Packaging and verification
10. Custom cards
11. Custom potions
12. Custom relics
13. Custom act events
14. Custom GUI

Use docs/handbook-overview.md as the handbook table of contents. The appendices contain compact API and package references.

Publishing

Pushes to main that change docs/, README.md, mkdocs.yml, the documentation dependencies, or the deployment workflow automatically:

1. run mkdocs build --strict
2. publish the generated site to gh-pages
3. trigger GitHub Pages deployment from the gh-pages branch root

No local MkDocs deployment command is required for a normal release.

Not Covered

This tutorial does not teach C#, Harmony, Godot, illustration, or game design from first principles. It documents how those tools connect to the current STS2 runtime.

License

MIT