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

{
  "type": "minecraft:crafting_shaped",
  "category": "equipment",
  "key": {
    "W": {
      "tag": "minecraft:planks"
    },
    "o": {
      "item": "minecraft:iron_ingot"
    }
  },
  "pattern": [
    "WoW",
    "WWW",
    " W "
  ],
  "result": {
    "item": "minecraft:shield"
  }
}