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Grim Anticheat

Grim Anticheat

v2.3.74-85dd3d9
Modrinth • 458 followers • 542 718 downloads
by Project author
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Fully async, multithreaded, predictive, open source, 3.01 reach, 1.005 timer, 0.01% speed, 99.99% antikb, "bypassable" 1.8-1.21 anticheat

Product

About

GrimAC

GrimAC is an free open source Minecraft anticheat designed to support the latest versions of Minecraft. It currently supports minecraft versions 1.8-1.21. Geyser players are fully exempt.

This project is considered feature-complete for the 2.0 (open-source) branch. If you would like a bug fix or enhancement and cannot sponsor the work, pull requests are welcome. A premium version is planned, which will offer additional subscription-based paid checks, such as heuristics.

Installation notes

  • Java 17 is now required. More information here.
  • Paper, Spigot, and Folia are currently supported.
  • If you use Geyser, place Floodgate on the backend server so grim can exempt bedrock players. Grim cannot access the Floodgate API if it is on the proxy.
  • If you use ViaVersion, it should be on the backend server as movement is highly dependent on client version.

Support & wiki information

Developer API

Grim's API allows you to integrate Grim into your own plugins.
- API repository: GrimAPI
- Wiki info: Wiki

How to compile

  1. git clone https://github.com/GrimAnticheat/Grim.git
  2. cd Grim
  3. ./gradlew build
  4. The final jar will compile into the build/libs folder

Grim supremacy

What makes Grim stand out against other anticheats?

Movement Simulation Engine

  • We have a 1:1 replication of the player's possible movements
  • This covers everything from basic walking, swimming, knockback, cobwebs, to bubble columns
  • It even covers riding entities from boats to pigs to striders
  • Built upon covering edge cases to confirm accuracy
  • 1.13+ clients on 1.13+ servers, 1.12- clients on 1.13+ servers, 1.13+ clients on 1.12- servers, and 1.12- clients on 1.12- servers are all supported regardless of the large technical changes between these versions.
  • The order of collisions depends on the client version and is correct
  • Accounts for minor bounding box differences between versions, for example:
    • Single glass panes will be a + shape for 1.7-1.8 players and * for 1.9+ players
    • 1.13+ clients on 1.8 servers see the + glass pane hitbox due to ViaVersion
    • Many other blocks have this extreme attention to detail.
    • Waterlogged blocks do not exist for 1.12 or below players
    • Blocks that do not exist in the client's version use ViaVersion's replacement block
    • Block data that cannot be translated to previous versions is replaced correctly
    • All vanilla collision boxes have been implemented

Fully asynchronous and multithreaded design

  • All movement checks and the overwhelming majority of listeners run on the netty thread
  • The anticheat can scale to many hundreds of players, if not more
  • Thread safety is carefully thought out
  • The next core allows for this design

Full world replication

  • The anticheat keeps a replica of the world for each player
  • The replica is created by listening to chunk data packets, block places, and block changes
  • On all versions, chunks are compressed to 16-64 kb per chunk using palettes
  • Using this cache, the anticheat can safely access the world state
  • Per player, the cache allows for multithreaded design
  • Sending players fake blocks with packets is safe and does not lead to falses
  • The world is recreated for each player to allow lag compensation
  • Client sided blocks cause no issues with packet based blocks. Block glitching does not false the anticheat.

Latency compensation

  • World changes are queued until they reach the player
  • This means breaking blocks under a player does not false the anticheat
  • Everything from flying status to movement speed will be latency compensated

Inventory compensation

  • The player's inventory is tracked to prevent ghost blocks at high latency, and other errors

Secure by design, not obscurity

  • All systems are designed to be highly secure and mathematically impossible to bypass
  • For example, the prediction engine knows all possible movements and cannot be bypassed
Environment

Requirements & compatibility

Compatibility & requirements

BukkitFabricFoliaPaperPurpurSpigot1.7.2 – 1.21.111.7.326.126.1.126.1.226.2

Local host

Unknown

Hosting on services

Unknown

Terms

License

Terms for using, modifying and redistributing this product.

GNU General Public License v3.0 or laterModrinth
Release

Latest release

v2.3.74-85dd3d9

23.07.2026 · Modrinth

Changes in this Build (since previous push)

Miscellaneous

  • Make duplicate handling more readable - by ManInMyVan (85dd3d9)