Packet Fixer | Stop Oversized Packet Disconnects

If you play heavily modded Minecraft, you have probably been booted from a server with a wall of text about packets. The world did not crash. A single network packet simply grew bigger than vanilla Minecraft allows, and the connection died on the spot. Packet Fixer raises those size caps so chunk data, item NBT and custom payloads arrive instead of getting tossed. Around 31 million downloads later, it has become one of those quietly essential mods that big packs ship with.

Oversized Packet and NBT Errors It Fixes

The official description names every disconnect message this mod is built to stop. If you have pasted one of these into a search bar, you are in the right place:

• "Tried to read NBT tag that was too big, tried to allocate X bytes where the max allowed is 2097152"
• "Badly compressed packet, size of X is larger than protocol maximum of 2097152"
• "Attempted to send packet over maximum protocol size: 8388608"
• "Chunk packet trying to allocate too much memory on read"
• "Packet too big (is X, should be less than 8388608)"
• "Payload may not be larger than 1048576 bytes"
• "Payload may not be larger than 32767 bytes"
• "Packet too large: size X is over 8"
• "Length wider than 21-bit"
• "Unable to fit X into 3"
• "Connection timeouts"
• "VarLong too big"
• "VarInt too big"

The project's own tagline puts it plainly. This is a simple mod that fixes problems with packets, NBT and timeouts.

Why Large Modpacks Hit These Limits

Vanilla caps how big a single packet can be, and that cap makes sense on a clean install where network data stays small. Add a few hundred mods and the math changes fast. Chunk packets carry more block and biome data (our Better Chunk Loading guide covers the travel side of chunk trouble). Items drag along bigger NBT tags. Custom mods push payloads of their own, and one of them eventually crosses the line. The server sees an oversized packet and drops the connection rather than risk corrupting data. Packet Fixer moves that ceiling so the same data arrives intact.

One note on scope. Recipe and tag errors are a separate family of problems, and the author routes those to a companion mod called Recipe Fixer. For the rest of the heavy pack experience, ModernFix targets launch times and RAM use, and it pairs well with this one.

Config Options and Performance Impact

You are not stuck with one set of hard coded numbers. Packet Fixer exposes the size limits in its config file, so server owners can tune how much headroom their setup gets. If a crowded pack still trips a cap, you can raise that limit instead of cutting mods.

Running it costs close to nothing. The jar itself is only about 30 KB, and the mod changes network limits rather than game behavior. It does not alter rendering or world generation in any way. Need support or want to follow development? The author runs a Discord server, linked on the official project page.

How to Install Packet Fixer

You need this mod on both sides of the connection. The official description says the client and the server each require it, so plan for two installs.

1. Start from a working loader install. Packet Fixer ships separate builds for Fabric, Forge, NeoForge and Quilt.
2. Download the build that matches your loader and game version from the download table on this page.
3. Drop the jar into your mods folder. If that folder does not exist yet, run the game once with your loader installed and it will appear.
4. Copy the same jar into the server's mods folder and restart the server.
5. Rejoin your world. Both sides now accept larger packets, and the disconnect spam should stop.

Packet Fixer FAQ

Does Packet Fixer need to be on both the client and the server?

Yes. The official description states the mod is required on client and server alike. If only one side raises the limits, oversized data can still end the connection.

Can I use Packet Fixer in my modpack?

Yes. The project is MIT licensed, and the author explicitly invites pack makers to include it. That is about as open as mod permissions get.

Can I change the packet size limits?

Yes. The limits are configurable in the mod's config file, so server owners can give a heavy pack extra headroom without editing game files.

Is Packet Fixer still updated?

Yes. TonimatasDEV maintains the project, and the latest release landed in September 2026. With roughly 31 million downloads, it is one of the most trusted fixes of its kind.

That is the whole story with this one. If you are new to adding jars to the game, our guide to installing Minecraft mods walks through every step, and our BadOptimizations writeup covers the FPS side of tuning a big pack.