OneGUI - Anti-Dupe & Inventory Security

OneGUI is a lightweight security plugin for Paper and Purpur 1.21+ servers designed to stop inventory duplication exploits. Many common dupe glitches rely on tricking the server into opening multiple menus at once, or interacting with a container while moving, turning around, or swapping items. OneGUI solves this by strictly enforcing a "one menu at a time" rule and instantly closing interfaces if suspicious client behavior is detected.

Why is this needed?

Cheaters often use packet exploits, intentional lag, or modified clients to desync their client from the server. By forcing a chest to stay open while their character is moving away, rotating, or scrolling through their hotbar, they can trick the server into duplicating items. OneGUI acts as a server-side check that shuts down these exact windows of opportunity.

Core Protections

• Single GUI Enforcement: The plugin tracks when a player has a menu open. If a client attempts to open a second inventory packet without properly closing the first one, the plugin cancels the action and forces all menus to close.
• Movement Detection: If a player moves their position or jumps while inside a chest, virtual GUI, or any inventory, the interface is closed instantly.
• Camera Rotation Tracking: If a player turns around or shifts their head angle (Yaw/Pitch) while looking at a menu, it breaks the connection. This stops headless packet injectors and macros that rotate the player away from a block while keeping a menu open.
• Hotbar Lockout: If a player changes their active hotbar slot (e.g., swapping from slot 3 to slot 4) while viewing an inventory, the container is forced shut immediately to stop slot-swapping exploits.

Configuration

You can toggle any of these checks in the config.yml file if they conflict with other plugins on your server:

checks:
  # Close GUI if player walks or jumps
  movement: true
  
  # Close GUI if player turns their head / camera view
  rotation: true
  
  # Close GUI if player changes their active hotbar slot
  hotbar: true

messages:
  reload: "&a[OneGUI] Configuration reloaded successfully!"
  no-permission: "&c[OneGUI] You do not have permission to execute this command."

Commands & Permissions

• /onegui reload - Reloads the configuration changes instantly without needing a server restart.
• Permission: onegui.admin (Defaults to server operators).