AntiBookBan

Paper anti-chunk ban plugin by Enea. A single jar compatible with Paper 1.21 → 1.26.2+.

What it does:

• /scan <player> — scans a player's inventory (including offline players) and reports shulker boxes that exceed the limit (default 2 MB).
• /fixall — scans all player data of all worlds (including offline players) and deletes shulker boxes that exceed the limit. Before each modification it creates a <uuid>.dat.bak backup.
• Book limits — a book can have at most 25 pages and ASCII characters only (blocks the "weird" characters used for the exploit).
• Automatic scan on join — if a player joins with a suspicious shulker, operators are notified.

Compatibility

Version	Player file	Status
1.21 – 26.0	<world>/playerdata/<uuid>.dat	✅ tested on 1.21
26.1 – 26.2+	<world>/players/data/<uuid>.dat	✅ tested on 26.2

The plugin is compiled against the Paper 1.21 API (Paper maintains backward compatibility) and uses only stable APIs: no NMS, so the same jar runs across the whole range. Adventure NBT is shaded into the jar (relocated), so it does not depend on the server's classpath.

Commands and permissions

Command	Description	Permission
/scan <player>	Scans inventory + armor + offhand + ender chest (online or offline)	antibookban.scan (op)
/fixall	Removes heavy shulkers from ALL player data (offline) and from online inventories	antibookban.fixall (op)
/abb reload	Reloads the config	antibookban.admin (op)

Other permissions: antibookban.notify (receives join alerts, op by default).

Configuration

max-shulker-size: 2097152   # shulker limit in bytes (2 MB)
max-book-pages: 25          # maximum book pages
ascii-only: true            # ASCII characters only in books
scan-on-join: true          # notify ops if a player joins with suspicious shulkers
fix-ender-chest: true       # /fixall also checks the ender chest

Note: ascii-only: true also blocks accented letters (è, à...). If you need them, set it to false.

How it works

• Online: each item is serialized to NBT with ItemStack#serializeAsBytes(); if a shulker exceeds the limit, it is reported/removed.
• Offline: .dat files are read/written directly with Adventure NBT (gzip), looking for shulkers in the Inventory and EnderItems lists and measuring the item's serialized NBT size. The infected files are precisely the huge ones, so an unlimited-size reader is used.

Future ideas

• Scan books in offline player data: /fixall currently removes only heavy shulkers; it could be extended to also remove books with too many pages/non-ASCII characters.
• Automatic removal on join: instead of alerting, remove the suspicious shulker immediately (config option).
• Detailed log: log file with date/time, player and slot for every removal.
• Whitelist/blacklist: exclude certain worlds or players from the scan.
• Discord/webhook notifications when /fixall finds something.
• bStats for usage statistics.