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1.8-1.20 support | 0.001% speed | 3.01 reach | 99.99% antikb | Open Source | 1.20 native

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This project is considered feature complete for the 2.0 open-source branch of this project. If you would like a bugfix or enhancement and cannot sponsor the work, pull requests are welcome. You can join the discord for jar releases & changelogs.

GrimAC is an open source Minecraft anticheat designed for 1.20 and supports 1.8-1.20. It is free while in beta. It will eventually become paid and/or will include offer additionally subscription based paid checks. Geyser players are fully exempt.

API Information

Grim's API allows you to integrate Grim into your own plugins. For more information, check out the API's github repository here.

Grim supremacy

Here are the main cores that make 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 safety 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


Published onNovember 21, 2023
Supports Folia

Pinned Versions