Long NBT Killer

Introduction

When Minecraft is encountering any compound / list nbt tag with a depth greater than 512, it throws an exception and refuses to load the save.

This mod replaced the annoying mechanism with a harmless log warning, and let the game go ahead.

Find the affected data (1.21.11+)

Look for Excessive NBT nesting in logs/latest.log. The warning includes the file, the depth reached and, when available, a path to the first compound or list that crosses the limit. Region warnings also include the dimension and chunk coordinates. A shortened path shows the beginning and end of the branch.

Minecraft normally rejects NBT nested beyond 512 levels. Some mods can add another layer to the same data each time a world is saved, so identify and update the mod that writes the data before repairing the save. Back up the world, then use the reported file and path in an NBT editor. For example, recursively nested terrain rules can be stored in level.dat on older worlds and in data/minecraft/world_gen_settings.dat on 26.x. See the terrain rule repair example.

Configuration (1.21.11+)

Edit config/longnbtkiller-common.toml on the server, or in your Minecraft instance for single-player.

The warning threshold remains 512 even when the configured read limit is higher. Back up the world before repairing it. Extremely deep data can still exhaust the Java stack during reading, world loading, or saving.

ATTENTION

• A compound / list nbt tag with a depth greater than 512 itself is abnormal, and you may check your save via NBT editor after receiving the warning in the log;
• You DEFINITELY CAN add the mod to your modpack.