Yarn
Yarn is a community driven set of open source Minecraft mappings that translate obfuscated Minecraft code into readable, human understandable names for mod developers.
Why are Mappings Important?
Section titled “Why are Mappings Important?”When Mojang compiles Minecraft, the source code is obfuscated. Classes, methods, and fields are renamed to short, generic identifiers such as a, b(), or c. This makes the code difficult for humans to understand.
Yarn provides human readable mappings for these names. Instead of calling an obfuscated method, you can write code like player.getHealth(), making mods much easier to develop, read, and maintain.