Getting Started with Slay the Spire Modding
ModTheSpire, BaseMod, Workshop subscriptions, and run-by-run mod selection
Slay the Spire modding is conceptually clean: install ModTheSpire and BaseMod as foundations, then add any number of content mods on top. This guide walks the standard install.
Step 1 — Install ModTheSpire
ModTheSpire is the JVM mod loader for Slay the Spire. Drop into the STS install directory.
Steam Workshop subscriptions of mods that depend on ModTheSpire trigger the same install pattern — the loader is the dependency.
Step 2 — Install BaseMod
BaseMod is the foundational framework most STS mods depend on. Drop into STS's mods/ folder.
After install, launching STS through ModTheSpire's launcher loads BaseMod and any installed mods.
Step 3 — Subscribe through Workshop
STS Workshop hosts most popular mods.
Three popular first picks:
- Hubris — large content overhaul. New characters, new mechanics, new events.
- Marisa Kirisame — fan-favourite custom character. Polished and well-balanced.
- Replay The Spire — comprehensive content addition: new events, cards, relics.
Subscribe; STS downloads to Documents/ModTheSpire/mods/ (or equivalent path depending on install setup).
Step 4 — Launch via ModTheSpire
ModTheSpire's launcher window shows your installed mods with checkboxes. Toggle which mods are active for the next run. Click Play to launch STS with those mods.
For a custom character mod: the character appears in the character-select screen alongside vanilla characters.
Step 5 — Run-by-run mod selection
STS's roguelike nature makes mid-run mod changes risky. ModTheSpire's launcher is where you change mod selection between runs.
Once a run starts, the mod set is fixed until that run ends (win, lose, or abandon).
Common gotchas
- Game launches without mods. You ran STS directly (via Steam) instead of through ModTheSpire's launcher. Always launch through ModTheSpire.
- Mod conflict with BaseMod version. BaseMod has had API changes. Some older mods need older BaseMod versions; some newer mods need the latest.
- Workshop mod missing. Subscribe delay. Restart Steam.
- Custom character missing options. Character mods sometimes lack the depth of vanilla characters. Set expectations.
If you've programmed in Java, STS modding is uniquely accessible — the source is human-readable, the API is well-documented, and the community is active. Many STS modders started as players who just wanted "one more card" and ended up building characters.