Modded servers sometimes kick players with errors about packets being too big. Minecraft limits how large a single packet can be, and some mods push past that limit.

Errors that point to this problem

• Tried to read NBT tag that was too big
• Badly compressed packet - size of ... is larger than protocol maximum
• Attempted to send packet over maximum protocol size
• Packet too big (is ..., should be less than 8388608)
• Payload may not be larger than 1048576 bytes
• Chunk Packet trying to allocate too much memory on read
• Internal Exception: io.netty.handler.codec.DecoderException: Failed to decode packet

Common causes

• Mods that conflict with each other, or outdated mods.
• Players using a different modpack version than the server.
• A single item holding huge data, such as a full backpack or storage drive.
• Very busy chunks, for example massive redstone or heavy world generation.
• Plain connection timeouts with no size error are usually the player’s own network, not the game.

Fix it

1. Reinstall the modpack on your own PC through your launcher. This clears corrupted local files and is the first thing to try.
2. Install Packet Fixer on the server. Download the version for your Minecraft version and mod loader from Modrinth, upload it to the mods folder using Files, and restart.
3. Install the same Packet Fixer on every player’s client. Put the jar in their mods folder. Players without it will not be able to join.
4. Restart the server and have everyone restart their game.

If the errors continue, open a ticket on our Discord  and include the full console log.