YSM Mapping API

Yes Steve Model changes its internal classes, methods and fields between builds, so integrations that rely on fixed obfuscated names break. Each time Minecraft starts, the library reads the bytecode layout of the YSM JAR that is present and passes the verified matches to dependent mods as typed symbols with semantic meaning. Consumer mods declare the symbols they need, and a newer YSM build that leaves a symbol unresolved is reported rather than guessed at.

The mappings it generates are stored in a mappings.json file that records the last successfully analyzed set. The symbols a mod has already requested stay in place until a fresh analysis finishes, and only then are they swapped out. Mixin-based integrations can use a supplied plugin, runtime reference mapper and wrapper with source aliases. The curated registry covers areas such as networking, client and server model synchronization, texture access, audio caches, player animation state, equipment hooks, bones and renderers.

Both 1.20.1 and 1.21.1 need Yes Steve Model at version 2.6.0 or later, and other mods that depend on this library rely on it as well. It runs on client and server and is published for Fabric, Forge and NeoForge, with files for 1.20.1 and 1.21.1, under the MIT License. Files are specific to one Minecraft version and loader, so the JAR must match the exact environment.