Data comes from extracting the game’s Godot pack and decompiling its C# assembly, then parsing to JSON for each game version. For bot builders the API is a ready source of card and monster data that tracks Early Access patches, and the run statistics give human pick and win rates to compare against.
Projects / Community tool
Spire Codex
Database and public API for Slay the Spire 2 (cards, relics, monsters, events and more in 15 languages), built from the game files, plus community run statistics, leaderboards and patch-to-patch diffs.