minecraft-assets/data/minecraft/loot_tables/gameplay/hero_of_the_village/librarian_gift.json

{
  "type": "minecraft:gift",
  "pools": [
    {
      "bonus_rolls": 0.0,
      "entries": [
        {
          "type": "minecraft:item",
          "name": "minecraft:book"
        }
      ],
      "rolls": 1.0
    }
  ]
}