Minecraft plugin GrimAC

🔌 About GrimAC

GrimAC is an open-source Minecraft anti-cheat plugin that implements a predictive movement simulation engine and asynchronous, multithreaded checks to detect client-side cheats. The project runs many checks on network threads, replicates player movement precisely, and includes lag compensation to reduce false positives. Official releases provide builds for Java Edition server environments.

🎯 Purpose

GrimAC's core purpose is to detect and mitigate cheating related to movement, timing, reach and other client-side exploits by reproducing possible player states on the server and comparing them to client-reported behavior. It is intended for server administrators who need automated detection and configurable punishments to keep gameplay fair.

⚙️ Features

• Predictive 1:1 movement simulation covering walking, swimming, knockback, cobwebs, bubble columns and entity riding.
• Asynchronous movement processing and multithreaded checks to reduce main-thread overhead.
• Lag compensation for player interactions to minimise false positives.
• Exemption handling for certain proxy or bridge scenarios (for example, explicit handling of Geyser players to avoid false positives).
• Developer plugin API for integrations and extensions.
• Open-source project with build artifacts and instructions to compile from source.

🧩 Who It Is For

• Server owners and administrators running Java Edition servers who want an open-source anti-cheat.
• Public or private survival/SMP and anarchy servers that require movement and combat enforcement.
• Developers and plugin authors who want to integrate anti-cheat checks via the provided API.

🏗️ Example Use Cases

• Enforcing fair PvP on a survival server by detecting extended reach and unusual speed.
• Preventing fly, step, or glide exploits on public servers while compensating for player lag.
• Integrating GrimAC's detections into moderation tools using the plugin API.

⚙️ Installation

📥 Setup

• Download the official plugin JAR for your server build.
• Place the JAR into the server plugins/ directory.
• Ensure the server runs Java 17 or higher and restart the server.
• Check server console/logs to confirm GrimAC loaded correctly.

📦 Dependencies

• If you use Geyser, install Floodgate on the backend where GrimAC runs so GrimAC can access the Floodgate API.
• If you use ViaVersion, install ViaVersion on the backend server only; GrimAC does not support ViaVersion being installed only on the proxy.

🛠 Compiling from source

• The repository includes build instructions; the official steps are: git clone https://github.com/GrimAnticheat/Grim.git, cd Grim, ./gradlew build. Built jars appear in the <platform>/build/libs folders.

🧠 Technical Notes

• The project distributes its source code and uses a GPL-family license.
• Official requirements include Java 17 or higher and a supported server environment (examples: Spigot, Paper, Folia, Fabric).
• The project provides nightly artifacts and a developer API for plugin integrations.
• The maintainers document that some builds and platforms are recommended from their release channels; consult the project's documentation for the correct artifact for your environment.

🤝 When This Plugin Is Useful

If you need a configurable, open-source anti-cheat focused on accurate movement simulation and asynchronous checks, GrimAC provides a developer-facing API, multi-environment builds, and explicit handling for common proxy/bridge scenarios, making it suitable for servers that require precise detection while aiming to reduce false positives.