Grim Anticheat

GrimAC is a free open-source Minecraft anticheat that supports the latest game versions. The modification is compatible with Minecraft versions from 1.8 to 1.21, with Geyser players being completely exempt from checks.

Currently, the project is considered fully functional within the 2.0 branch (open source). A premium version is planned, offering additional subscription-based features including heuristic checks.

Installation Features

• Java 17 is mandatory.
• Supports Paper, Spigot, and Folia.
• When using Geyser, place Floodgate on the backend server so Grim can properly handle Bedrock players.
• ViaVersion should be installed on the processing server since movement heavily depends on client version.

Key Advantages

Movement Simulation Engine

• Complete simulation of all possible player movements with 1:1 accuracy
• Handles everything: from basic walking and swimming to knockback, cobwebs, and bubble columns
• Support for riding various entities (boats, pigs, striders)
• Accounts for minor version differences, including hitbox and block variations

Asynchronous Multithreaded Architecture

• All movement checks and most listeners run in the netty thread
• Scalability for hundreds of players and beyond
• Carefully designed thread safety

Complete World Replication

• The anticheat creates an exact copy of the world for each player
• Chunk caching with efficient compression (16-64 KB per chunk)
• Safe work with world state and fake blocks
• Individual lag compensation for each player

Latency Compensation

• World changes are queued until the player receives them
• Breaking blocks under players doesn't trigger false positives
• Adjustment of flying status and movement speed

Reliable Protection

• Systems designed for maximum security
• Mathematically impossible to bypass prediction mechanisms
• Safe operation with various obstacles and client-side blocks