Yarn but it's Json

{
  "namespaces": [ "official", "intermediary", "named" ],
  "autoprefix": {
    "intermediary": "net/minecraft/",
    "named": "net/minecraft/"
  },
  "mappings": {
    "classes": [
      {
        "official": "b",
        "intermediary": "class_1159",
        "named": "util/math/Matrix4f"
      },
      {
        "official": "g",
        "intermediary": "class_1160",
        "named": "client/util/math/Vector3f"
      }
    ]
  }
}