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

{
  "type": "minecraft:crafting_shaped",
  "group": "banner",
  "pattern": [
    "###",
    "###",
    " | "
  ],
  "key": {
    "#": {
      "item": "minecraft:yellow_wool"
    },
    "|": {
      "item": "minecraft:stick"
    }
  },
  "result": {
    "item": "minecraft:yellow_banner"
  }
}