Stackable Enchanted Books

A small Fabric mod for Minecraft 1.21.1. Identical enchanted books stack up to 16 instead of 1 — you can raise or lower that limit in the config.

Enchanted books that are actually identical (same enchantments, same levels, same anvil work penalty, same custom name, same everything else) pile up in your inventory and shulker boxes like any other item. Books that differ in any way still take separate slots, exactly like vanilla.

Features

• Identical enchanted books stack, up to a configurable limit (default 16).
• The anvil and the grindstone are updated to work on one book of a stack at a time, so a stack is never duplicated or destroyed in a single operation.
• No other item is affected. Only enchanted books get the new stacking behavior.
• No registry changes, no new items, no new blocks — just a default item component tweak plus the container fixes needed to keep it safe.

What counts as "identical"

Two enchanted books stack together only when the game itself considers them the exact same item: ItemStack.isSameItemSameComponents. In practice that means the same stored enchantments at the same levels, the same anvil repair cost, the same custom name, and any other component matching. A Sharpness I book will never stack with a Sharpness II book or with an Unbreaking I book. The mod doesn't add any merging logic beyond what vanilla already checks for "is this the same item".

Anvil and grindstone behavior

Vanilla assumes every enchanted book has a count of 1. Without extra care, letting books stack would mean losing whole stacks to a single anvil pull or duplicating them in creative mode. This mod changes the relevant vanilla code paths so stacks are always handled one book at a time:

Everything else that touches books — the enchanting table (single-item slot, and enchanted books can't be enchanted anyway), the chiseled bookshelf, lecterns, loot tables, and villager trades — already worked correctly with stackable books and needed no changes.

Configuration

The mod creates config/stackable_enchanted_books.json on first launch:

{
  "maxStackSize": 16
}

• The file is read once on startup — restart the game or server after changing it.
• An invalid value (bad JSON, wrong type, a fraction, NaN, or out of range) logs one warning and falls back to 16. The mod never rewrites or "fixes" your file for you.
• On every start, the mod logs one line stating the value in effect, e.g. Enchanted books stack up to 16.

Requirements

• Minecraft 1.21.1
• Fabric Loader 0.16.0 or newer
• Fabric API
• Java 21

Install on both sides, with the same value

This mod changes a default item component, which isn't something the network syncs between client and server. Install it on the server and on every client, using the same maxStackSize.

If a client and server end up mismatched anyway (nothing prevents it — the mod adds no registry entries or packets to check for), here's what actually happens, verified against the 1.21.1 source:

• Survival/adventure inventories and containers: the server is authoritative and sends back the correct slot contents, so at worst you'll see a visual glitch — books that seem to merge and then snap back, or an anvil/grindstone preview that's briefly wrong. Nothing is duplicated or lost.
• Creative mode: the server rejects a creative slot update above its configured limit, so a client with a higher limit can see a picked-up stack vanish. This is specific to creative inventory handling.
• Uninstalling later: worlds still load fine. Vanilla itself accepts saved stacks above an item's normal limit (up to 99), so existing book stacks just sit as they are until you move or split them.

Compatibility and limitations

• The mod is built on four small, targeted mixins (into AnvilMenu, GrindstoneMenu, the grindstone result slot, and one hook in AbstractContainerMenu.broadcastChanges) plus Fabric API's DefaultItemComponentEvents.
• Mods that replace vanilla's anvil or grindstone logic outright (anvil overhauls, "no too expensive" mods, custom grindstone implementations) or that add their own separate book-consuming machines are not covered by these mixins.
• This is intentional: if another mod overwrites the exact vanilla methods this mod hooks into, Mixin will fail loudly and stop the game at startup, rather than silently letting a dupe or item-loss bug slip through.
• Enchanted books in a bundle (experimental in 1.21.1) now take up 1/16 of the bundle each instead of filling the whole bundle.