minecraft-assets/data/minecraft/recipes/blue_carpet_from_white_carpet.json

{
  "type": "minecraft:crafting_shaped",
  "category": "misc",
  "group": "carpet",
  "key": {
    "#": {
      "item": "minecraft:white_carpet"
    },
    "$": {
      "item": "minecraft:blue_dye"
    }
  },
  "pattern": [
    "###",
    "#$#",
    "###"
  ],
  "result": {
    "count": 8,
    "item": "minecraft:blue_carpet"
  }
}