🛡️ GuardAC — lightweight anti-cheat for 1.21 and 26.x

GuardAC is a 24-check anti-cheat for Paper, Spigot, Bukkit, Purpur and Leaf servers running Minecraft 1.21 – 1.21.11 and 26.1 – 26.3. It covers combat, movement, world and inventory cheats, and it stops Meteor-style mace one-shots.

• 📦 One small jar (~90 KB) for every server type, with no ProtocolLib, no NMS and no dependencies.
• ⚡ Lightweight and lag-aware. It measures TPS itself and pauses movement checks during lag. In a live profile it used about 0.2% of the server thread.
• 🆕 Ready for 26.x. The same jar runs on 1.21 (Java 21) and 26.1 – 26.3 (Java 25). It understands spears (longer reach, lunges and charges), happy ghasts, new mounts, wind charges and the mace.
• 🎯 Uses real player stats. Movement speed, attack reach, block reach and step height come from the player's actual attributes, so potions, Soul Speed, items and skill plugins like AuraSkills are allowed for automatically.

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🔍 The 24 checks

⚔️ Combat

Check	Catches
Reach	Hitting from too far away (ping-compensated, spear reach respected)
KillAura	Hitting targets outside the player's view, or several targets in one tick
MaceKill	Fake-fall mace smashes. A smash only counts if the attacker really fell
AutoClicker	Clicking too fast, or with timing too regular to be human
Velocity	Anti-knockback: not moving after being hit or pushed
AutoTotem	A new totem in the off hand within a tick or two of one popping

🏃 Movement

Check	Catches
Speed	Speed hacks and bhop
Fly	Fly, hover, airwalk
NoFall	Claiming to be on the ground mid-air to avoid fall damage
Step	Walking straight up blocks without jumping
Spider	Climbing walls without ladders, vines or scaffolding
Jesus	Walking on water or lava
NoSlow	Full speed while eating, blocking or drawing a bow
Timer	Speeding up the game clock
ElytraFly	Climbing or hovering on an elytra without rockets
InventoryMove	Walking with a chest or menu open
BadRotation	Impossible head angles

⛏️ World and inventory

Check	Catches
FastBreak	Mining faster than the tool, enchantments and effects allow (Nuker, FastMine)
BlockReach	Mining or placing blocks out of reach
Scaffold	Placing blocks without looking at them
FastPlace	Placing blocks faster than a person can click
XRay	Alerts staff when someone finds rare ore veins while mining almost no stone
FastEat	Eating faster than normal
FastInventory	Chest stealers, inventory cleaners, auto-armor

How MaceKill works

A mace smash does more damage the further the attacker fell, and the server takes the fall from what the player's game tells it. Cheats tell the server "I fell 20 blocks" in one or two messages, then hit. A real 20-block fall takes about 24 ticks of gravity. GuardAC checks that the attacker is actually in the air and has been airborne long enough for the fall they claim. If not, the hit is cancelled.

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🧯 False-flag protection

• Safe updates: a check that isn't in your config.yml yet runs in alert-only mode. Updating GuardAC can never start kicking or banning players by surprise.
• Bedrock (Geyser) players are detected automatically and skipped by checks based on where the crosshair points.
• Never checked: creative and spectator players, and anyone with guardac.bypass.
• Movement allowed for: flying, elytra, riptide, mounts, swimming, climbing, levitation and slow falling. Liquids, cobwebs, scaffolding, powder snow and bubble columns don't cause movement flags.
• Grace periods after joining, respawning, teleporting, knockback, explosions, wind charges and spear lunges.
• Plugin-broken blocks (3x3 pickaxes, vein miners) are never counted as FastBreak.
• Violation levels drop over time, so a single odd flag never punishes anyone.

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⚖️ What happens when a player flags

1. Alert: staff see it in chat, and it goes to the console and violations.log.
2. Setback: movement is pulled back, and suspicious hits, block breaks, placements and eating are cancelled.
3. Punishment: at the configured violation level, the check's command runs (a kick by default).

Optional punishment ladder

Turn it on to escalate punishments, for example 14 days → 30 days → permanent + IP ban. Every step is a console command you choose, so it works with EssentialsX, LiteBans or vanilla bans. Each player's offence history is saved and survives restarts.

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💬 Commands

Shortcuts: /gac, /anticheat

Command	Description
/guardac alerts	Turn alerts on or off for yourself
/guardac status	Server TPS and which checks are on
/guardac vl <player>	A player's violation levels
/guardac reset <player>	Clear a player's violation levels
/guardac offenses <player>	A player's punishment history (works offline)
/guardac resetoffenses <player>	Clear a player's punishment history
/guardac reload	Reload the config

🔑 Permissions

Permission	Default	Description
guardac.admin	OP	All commands (includes alerts)
guardac.alerts	OP	Receive cheat alerts
guardac.bypass	Nobody	Skip all checks

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📥 Installation

1. Drop GuardAC-1.0.0.jar into your plugins folder.
2. Restart the server.
3. Adjust plugins/GuardAC/config.yml and run /guardac reload.

💡 Tip: for the first few days, set every max-vl to 0. You'll get alerts only, so you can tune the limits for your server before anyone is kicked.

⚠️ Good to know

• Normal events, not network packets. GuardAC works through the server's normal events, which keeps it light. The very largest packet-level anti-cheats can catch a few extra cheat types, such as Blink, Backtrack and advanced Timer bypasses.
• Some cheats can't be caught by any anti-cheat, because they only change what the cheater sees: ESP, tracers, freecam and chest ESP. For X-ray, also turn on Paper's built-in anti-xray. GuardAC's XRay check adds alerts based on mining behaviour.

This is the first release. If you see a false flag, please report it with the alert text from violations.log.

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© 2026 KhangPlayMusic. All rights reserved. Free to use on any server. Please don't re-upload or resell it.