GrimAnticheat/Grim

What it does

GrimAC is an open-source anticheat plugin for Minecraft servers. Instead of comparing players against simple speed or reach thresholds, it runs a movement simulation that reproduces the player's possible positions and collisions, including version-specific hitboxes and block behavior, and flags actions the simulation cannot explain. It also keeps a per-player replica of the world so checks can run against a consistent state and support latency and inventory compensation.

The design is fully asynchronous: movement checks and most listeners run on the Netty thread, which the project says lets it scale to hundreds of players. It targets server operators running Spigot, Paper, Folia, or Fabric who need cheat detection on current Minecraft versions. Geyser players are fully exempt to avoid false positives.

Quick start

Prepare a Spigot, Paper, Folia, or Fabric server with Java 17 or newer. Download the plugin from Modrinth, which the project recommends, or grab the latest Bukkit or Fabric build artifacts from the Bukkit artifact and the Fabric artifact. Drop the jar into the server's plugins folder and restart.

If the server sits behind Velocity or BungeeCord, install Floodgate on the backend server when using Geyser, and install ViaVersion only on the backend server, not on the proxy. The supported-environment wiki page explains these cases in detail; the documentation wiki and FAQ cover configuration and common questions.

To build from source, run:

git clone https://github.com/GrimAnticheat/Grim.git
cd Grim
./gradlew build

The resulting jars appear under each platform's build/libs folder. The project's contributing guide covers pull requests, and the GrimAPI repository documents integrating Grim into other plugins.

Constraints

Java 17+ is required, and the server must be Spigot, Paper, Folia, or Fabric. With proxies, ViaVersion must not be installed on the proxy even if it is also installed on the backend. The 2.0 open-source branch is described as feature-complete; new bug fixes and enhancements are handled through sponsored work or pull requests. A premium subscription version with additional checks such as heuristics is planned, so some future checks may not be part of this repository. Geyser players are exempt, which means they receive no anticheat coverage. The project is licensed under GPL-3.0.

HotRepo's take

Grim appeared on the Java daily list on 2026-11-14 at position 9 with 6 stars gained that day, against a total of 1,810 stars and 695 forks. That single snapshot shows it still attracting some attention in the Java ecosystem, but there is no recorded all-language daily rank and no usable trend series here, so the data only supports a same-day observation rather than a claim about sustained momentum. The interesting technical bet is the choice to model movement and collisions per client version rather than rely on threshold checks, which is what the project credits for its cross-version behavior; operators running mixed-version or proxy setups should weigh the ViaVersion backend-only requirement before deploying.