Minecraft wiki entry for Creating_Forge_mods, associated text: There are two different sets of mappings available for method names - "MCP" community-based mappings, and "Official" mappings based in part on the official Obfuscation maps (though class names are different for technical reasons). The default in the MDK has recently been changed to 'official', but this tutorial will use the MCP mappings for now because function parameter names are not available in the official mappings.