minecraft-assets/assets/minecraft/recipes/string_to_wool.json

{
  "type": "crafting_shaped",
  "pattern": [
    "##",
    "##"
  ],
  "key": {
    "#": {
      "item": "minecraft:string"
    }
  },
  "result": {
    "item": "minecraft:wool",
    "data": 0
  }
}