Packet Logger

A deep packet logging mod for Minecraft Fabric that captures all network traffic (´S2C´ and ´C2S´) with full NBT/Component data.

Use Cases

• Mod Development: Debug network communication between client and server
• Container Inspection: View exact contents of inventories with full NBT/Component data and copying them
• Reverse Engineering: Analyze server-side mechanics and packet structures
• Anti-Cheat Analysis: Understand what data the server sends and receives
• Learning: Understand how Minecraft's network protocol works

Usage

Keybind

Press F6 to open the config screen.

You can also assign a keybind in the config screen to toggle packet logging on/off. It is unbound by default.

Packet Selection

Use the dual-list selector to choose which packets to log:

• S2C (Server → Client): Incoming packets like inventory updates, entity spawns, etc.
• C2S (Client → Server): Outgoing packets like clicks, movements, etc.

Log Modes

• Chat: Display packets in the game chat (truncated for readability)
• File: Save packets to log files with full data

Log Files

Logs are saved to:

MINECRAFT_FOLDER/packet-logger/packets_2026-01-04_15-30-45_servername.log

A new log file is created when:

• Joining a world/server
• Re-enabling logging after it was disabled

Example Output

[12:34:56.789] [S2C] InventoryS2CPacket {syncId:2,revision:1,id:"minecraft:generic_9x3",components:{"minecraft:container":[{item:{id:"minecraft:diamond_sword",count:1,components:{"minecraft:enchantments":{levels:{"minecraft:sharpness":5}}}},slot:0}]}}

Configuration

Config saved at: .minecraft/config/packet-logger-config.json

{
  "logPackets": true,
  "logMode": "FILE",
  "deepLogging": true,
  "loggingKeybind": -1,
  "selectedS2CPackets": ["InventoryS2CPacket"],
  "selectedC2SPackets": ["ClickSlotC2SPacket"]
}

Installation

Requirements

• Minecraft 1.21 - 1.21.11
• Fabric Loader 0.16.0+
• Fabric API

Download

You can download the mod from Modrinth. Simply place the downloaded .jar file into your .minecraft/mods folder.

Download on Modrinth

For Developers

Building

./gradlew build

Output: build/libs/packet-logger-1.1.2.jar

Project Structure

src/main/java/dev/redstone/packetlogger/
├── PacketLoggerClient.java       # Client entrypoint
├── config/
│   └── ModConfig.java            # Configuration
├── logger/
│   ├── PacketLogger.java         # Main logger
│   └── unpacker/                 # Specialized packet unpackers
│       ├── ItemStackFormatter.java
│       ├── InventoryS2CUnpacker.java
│       └── ...
├── mixin/client/
│   ├── ClientConnectionMixin.java # Packet interception
│   └── ...
└── screen/
    └── SimpleConfigScreen.java    # Config UI

Available Packets

All packets are loaded dynamically from the game's PacketType registries and are selectable in the config screen's dual-list selector. Both S2C (Server → Client) and C2S (Client → Server) packets are covered across all protocol phases.

See PACKETS-1.21.4.md for an example listing of all packets for Minecraft 1.21.4.

License

This project is licensed under the GNU General Public License v3.0.