AntiCheat — Bukkit 1.21.11

A lightweight, production-ready anti-cheat plugin focused on fly detection with automatic 30-day bans.

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Installation

1. Drop AntiCheat-1.0.0.jar into your server's plugins/ folder.
2. Start/restart the server.
3. Edit plugins/AntiCheat/config.yml to tune thresholds.
4. Run /anticheat reload to apply changes without a restart.

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How Fly Detection Works

Check	Trigger
Fly[UpVelocity]	Player moves upward faster than vanilla allows
Fly[Hover]	Player stays airborne with no Y-movement for 20+ ticks
Fly[UpInAir]	Player moves upward while already airborne
Fly[ToggleFlight]	Client enables flight without server permission

When VL reaches the threshold (default 10), the player is:

• Kicked immediately
• Banned for 30 days via Bukkit's ban list
• Ban screen reads: "Using a modified client"
• All online players see a broadcast

False-Positive Mitigation

Grace periods are automatically applied for:

• Jumping (6 ticks)
• Taking damage / knockback (10 ticks)
• Teleporting (20 ticks)
• Joining the server (60 ticks = 3 seconds)
• Levitation potion
• Elytra gliding
• Being in or near liquid
• Being on climbable blocks (ladders, vines, scaffolding, etc.)
• Creative / Spectator mode
• Server-granted flight (/fly, etc.)

VL also decays over time (every 40 ticks by default) so legitimate players don't accumulate false flags.

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Commands

Command	Description	Permission
/anticheat reload	Reload config	anticheat.admin
/anticheat status	Show plugin info	anticheat.admin
/anticheat vl <player>	Check a player's VL	anticheat.admin
/anticheat whitelist add/remove <player>	Manage bypass	anticheat.admin

Permissions

Permission	Default	Description
anticheat.admin	OP	Access to all commands
anticheat.bypass	false	Exempt from all checks

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Configuration

See config.yml for full options. Key values:

settings:
  fly-vl-threshold: 10       # VL points before ban
  vl-decay-ticks: 40         # How often VL decreases
  max-upward-velocity: 0.42  # Max allowed Y velocity per tick

ban:
  duration-days: 30
  reason: "..."              # Supports & color codes and \n newlines

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Tuning Tips

• Too many false positives? Increase fly-vl-threshold to 15–20 and increase grace tick values.
• Too lenient? Lower fly-vl-threshold to 6–8.
• Enable debug mode (debug.enabled: true) to watch VL accumulate in real time.
• Grant anticheat.bypass to trusted staff via your permissions plugin (LuckPerms, etc.).