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

{
  "type": "crafting_shaped",
  "pattern": [
    "###",
    "# #",
    "#R#"
  ],
  "key": {
    "R": {
      "item": "minecraft:redstone"
    },
    "#": {
      "item": "minecraft:cobblestone"
    }
  },
  "result": {
    "item": "minecraft:dropper"
  }
}