ModDetector

ModDetector

Packet-level cheat mod detection for Minecraft servers. Identifies disallowed client modifications using a translation key exploit — without any client-side agent.

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How it works

The plugin exploits Minecraft's sign editing flow to probe the client's translation table. If a mod is installed, it replaces translation keys with its own strings — betraying its presence.

Detection flow (at connection time):

1. A BlockUpdatePacket is sent to place a virtual sign near the player
2. An OpenSignEditorPacket is sent, opening the sign editor on the client
3. A SignUpdatePacket is sent containing the mod's translation key as the sign text
4. The client echoes the sign content back — if the value differs from the default fallback, the mod is present

The entire handshake is invisible to the player and occurs silently at connection time. No GUI is shown, no chat messages are sent during detection.

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Detected mods

The following mods are blocked out of the box. You can extend the list in config.yml.

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Configuration

All settings live in plugins/ModDetector/config.yml.

# Fallback value used to detect mod presence
default: "fallb"

# Message shown to the player on detection
# Supports MiniMessage, modern & legacy ampersand codes
kick-message:
  - "&cYou are using a cheat mod that is not allowed on [Your Server] (%mod%!), if you join"
  - "with this again you will be banned!"

# Mod translation keys to detect
disallowed-mods:
  "Meteor": "key.meteor-client.open-gui"
  "Item Scroller": "itemscroller.gui.button.config_gui.generic"
  "Freecam": "key.freecam.toggle"
  "Accurate Block Placement": "text.autoconfig.accurateblockplacement.title"

# Enable packet & result logging for debugging
debug: false

Color code support

The kick-message field supports all three Minecraft color systems:

• MiniMessage — <red>, <#ff4455>
• Modern ampersand — &c, &#ff4455
• Legacy ampersand — &c, &x&f&f&4&4&5&5

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Adding custom mods

Any mod that registers Minecraft translation keys can be detected. Find the key in the mod's language files (usually in assets/<modid>/lang/en_us.json) and add it to disallowed-mods:

disallowed-mods:
  "Your Mod Name": "your.mod.translation.key"

Note: The default field must be set to a string that is never a valid translation output — the default "fallb" is safe for vanilla clients. Do not change it unless you understand the detection logic.

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Requirements

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Installation

1. Download and place ModDetector.jar into your plugins/ folder
2. Download PacketEvents and place it in plugins/ as well
3. Start the server — config.yml will be generated automatically
4. Edit config.yml to configure your kick message and disallowed mods
5. Reload with /reload or restart the server

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*Inspired by PvPClub's detection approach. *