Villager trade-trade

Right-clicking a librarian holding an enchanted book makes the villager consume the book and add it to his trade list, where anyone can buy that exact book back for emeralds. The mod turns books into a currency that the local librarian treats as an actual dealer's stock, so a world's enchanted book market grows from what players bring in.

When a librarian already offers a book with the same enchantment type, handing over another one does not add a second trade. Instead the existing trade is rerolled with a new random price, and the stock adjusts to the level that was handed over. Restocking works as usual, so each reroll is a gamble. Books with several enchantments and custom NBT are not accepted, which keeps pricing predictable. A single villager can learn up to five different enchantment types, each in its own trade slot. Other professions, and unemployed villagers, ignore a book and keep it in hand.

The server runs the gameplay logic, while client-side code is used only for rendering, so the mod works in singleplayer and on dedicated servers. A current Fabric API and Fabric Loader are needed, along with a recent Minecraft 26.2 build or newer, and the mod is published for 26.2 and 26.3 under the MIT License.