Iustitia Anti-Cheat
by Thoria
Iustitia Anti-Cheat is a Fabric client mod that watches other players on the same client for signs of cheating and records what it sees.
What it does
The mod runs only on the client and checks other players' movement, combat, rotation and packets while they are tracked, so no server install or extra permissions are needed. Because it reads what the server already sends, it works on vanilla servers, minigame networks and realms alike. Each tracked player is given a cheat tier that appears above their nametag, and a moderator decides what to do with it.
Iustitia is open source under the MIT License and is published for Fabric only, with a single game version: 1.21.11, where the latest file is 1.4.0 from 2026-09-21. It requires Fabric API, Fabric Language Kotlin and YetAnotherConfigLib (YACL) to run. Public source code, an issue tracker and a wiki are linked from its project page.
Key features
Checks with lag awareness
Movement checks are paused during lag spikes, which the mod names as the main source of false positives, and tiers stay conservative until corroborated.
Pose-aware hitboxes
Hitboxes adjust for crouching, prone, and elytra flight so that legitimate reach and target alerts are less likely to trip.
Live side panels
A corner overlay holds live side panels for the player's transcript and chat history, and the game keeps running behind it.
Evidence clips
A moderator can export the final seconds of positions and alerts as a portable .iusclip file, then hand it to another moderator who replays it later.
Directional sonar
An alert plays a note whose pan shows the direction of the suspect and whose pitch shows the distance, so the moderator can keep watching the scene.
Gallery
Compatibility
Latest build for each game version and loader.
Only full game releases are shown. This mod publishes no snapshot builds.
Requirements
Dependencies declared by the latest file for each loader.
Required 3
Use cases
Who it’s for: Moderators and server staff who want a client-side tool to watch other players, collect evidence and document cases from the same client, without needing access to the server.
How it compares
KsAntiCheat is a Fabric mod for 1.21.1 that runs on the client and server together under the MIT License, and it is not open source. Moderation Log is a client-side Fabric mod for 1.21.11 under the MIT License, also not open source. Anti Darkness is client-side only and open source under the MIT License, covering 1.21.7 – 1.21.11.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| Iustitia Anti-Cheat | Fabric | 1.21.11 | Client-side only | 2026-09-21 |
| KsAntiCheat | Fabric | 1.21.1 | Client and server | 2026-08-10 |
| Moderation Log | Fabric | 1.21.11 | Client-side only | 2026-05-27 |
| Anti Darkness | Fabric | 1.21.7 – 1.21.11 | Client-side only | 2026-08-14 |
Questions
Does Iustitia Anti-Cheat need to be installed on the server?
Which dependencies are required?
Which game versions does the mod support?
In the catalog
Iustitia Anti-Cheat is one of 8,016 Management mods on ModsFinder, and one of 5,930 Management mods for Fabric. 19,862 mods support Minecraft 1.21.11.
More from Thoria
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What the author says
Justice, Observed. A client-sided anticheat for Minecraft 1.21.11 (Fabric) that watches other players from your own client. No server install, no permissions needed, no outgoing packets, no telemetry. It just watches what the server already sends you and turns it into clear, trustworthy cheat detection. Most…
Official listing
- Modrinth page
- modrinth.com/mod/iustitia
- Owner
- Thoria
- Published
- 2026-06-27
- Updated on Modrinth
- 2026-09-21
- Facts verified
- 2026-10-15