Grim Anticheat
Prediction-based anti-cheat. Simulates player movement server-side and compares it with client packets for accurate cheat detection.
Anti-CheatWhat is Grim Anticheat?
Grim Anticheat takes a prediction-based approach that sets it apart from threshold-counting anti-cheats. For movement, it simulates server-side what the player should be able to do given their inputs and the world, then compares that prediction to the packets the client actually sends — a deviation reveals cheating with very few false positives. It also covers combat, timer and vehicle checks. It is open-source and free, runs on Spigot/Paper, and is widely regarded for accurate movement detection. Tuning is still required, but its prediction model means it flags far less legitimate play than older designs.
Who it's for: PvP, survival and competitive servers that want strong, low-false-positive cheat detection without a premium licence. Popular with technically-minded owners who value its prediction engine. It is built and maintained by GrimAC and sits in the anti-cheat category.
Key features of Grim Anticheat
- Prediction engine
- Movement simulation
- Combat checks
- Timer checks
- Vehicle checks
- Configurable punishments
- Verbose logging
- Low false-positive rate
How to install Grim Anticheat
Grim Anticheat runs on Spigot or Paper servers. The GrimAC project maintains Grim for current Spigot/Paper versions and updates actively; use a build matching your server version.
- 1Stop your server, or have it ready to restart. Always back up your world and plugins folder before adding a new plugin.
- 2Download GrimAnticheat.jar (a build matching your server version) and place it in your server's /plugins folder.
- 3Grim Anticheat has no required dependencies, so it runs on its own once the jar is in place.
- 4Start the server fully. Grim Anticheat generates its configuration files on first launch — stop the server, edit them to taste, then start again.
- 5Confirm it loaded by checking the console for Grim Anticheat on startup, or by running one of its commands in-game.
Note: Drop Grim into /plugins and restart — it works out of the box with strong defaults and needs no ProtocolLib (it bundles its own packet handling). Review alert and punishment settings before enabling auto-bans, and use /grim debug on a test account to understand flags, since prediction tuning differs from threshold tuning.
Grim Anticheat commands and permissions
Main commands
/grim alerts- Toggles staff alerts for detected violations.
/grim debug- Streams detailed prediction data for a player, the primary tool for investigating flags.
/grim perf- Shows Grim's performance impact so you can confirm it is running efficiently.
/grim reload- Reloads Grim's configuration.
Permission nodes
grim.alerts- Allows receiving violation alerts; give to staff.
grim.debug- Allows using the debug output for investigation.
grim.exempt- Exempts the holder from checks; assign sparingly.
Grim Anticheat FAQ
What makes Grim different from other anti-cheats?
Grim is prediction-based: it simulates the player's possible movement server-side and compares it to what the client actually does, rather than counting violations against a threshold. This gives it very accurate movement detection with a low false-positive rate, which is why it is well regarded for catching movement and timer cheats.
Is Grim free?
Yes. Grim is open-source and free, which is unusual for an anti-cheat of its capability — many comparable options are premium. Being open-source also means its checks are publicly auditable, and it is actively developed by the community.
Does Grim need ProtocolLib?
No. Grim handles packets itself and does not require ProtocolLib, which simplifies installation and avoids a version-sensitive dependency. You just install Grim and it operates independently.
Will Grim falsely flag laggy players?
Its prediction model is specifically designed to tolerate latency far better than threshold-based systems, so false positives are rare. They are not impossible on extreme lag or with certain unusual movement plugins, so review alerts and use /grim debug before turning on automatic punishments.
Does Grim catch combat cheats like kill-aura?
Yes. Alongside its standout movement detection, Grim includes combat checks (such as reach and rotation/aim anomalies), timer checks and vehicle checks. Coverage continues to expand; its movement and timer detection are its most acclaimed strengths.
Features
- Prediction engine
- Movement simulation
- Combat checks
- Timer checks
- Vehicle checks
- Configurable punishments
- Verbose logging
- Low false-positive rate
Commands
/grim alerts/grim debug/grim perf/grim reloadPermissions
grim.alertsgrim.debuggrim.brandgrim.exempt