ModsFinder

DEUF - Duplicate Entity UUID Fix [NeoForge]

by KreloX

DEUF - Duplicate Entity UUID Fix is a server-side NeoForge mod that stops a warning about duplicate entity UUIDs from flooding the server console.

NeoForgeServer-side onlyMIT LicenseOpen source1.21.1 – 26.1

What it does

When a world loads, entities that already carry a UUID can collide with others, and the server logs a line for each conflict, often many lines per restart. DEUF gives the affected entity a fresh, non-duplicate UUID so the message no longer appears. Once a world has been loaded with the mod, reloading the world or restarting the server no longer produces the repeated message for that entity.

The mod is intended for servers that run older worlds, where the warning tends to appear most. Installation is a single file placed in the mods folder of the server, and the mod runs server-side only, so players join without installing anything. Files are published for NeoForge across 12 release versions, 1.21.1 – 26.1, and the code is open source under the MIT License, with a source repository and an issue tracker linked from the project page.

Key features

  1. Fresh UUIDs for conflicting entities

    Entities whose UUIDs are already in use are given a new UUID when their chunk loads, which removes the duplicate.

  2. Less console spam

    The repeated log line naming the entity and its existing UUID stops appearing once the conflict is resolved.

  3. Ported from an earlier mod

    The NeoForge build of DEUF is a port of CASual TY's DEUF, carried over under the MIT License.

Compatibility

Latest build for each game version and loader.

26.x1 of 1 version with builds
26.126.1-1.0
1.21.x11 of 11 versions with builds
1.21.111.21.1-1.0
1.21.101.21.1-1.0
1.21.91.21.1-1.0
1.21.81.21.1-1.0
1.21.71.21.1-1.0
1.21.61.21.1-1.0
1.21.51.21.1-1.0
1.21.41.21.1-1.0
1.21.31.21.1-1.0
1.21.21.21.1-1.0
1.21.11.21.1-1.0
ReleaseBetaAlphaNot available

Only full game releases are shown. This mod publishes no snapshot builds.

Use cases

Older server worlds

Servers that keep a world from an earlier version, where entities were saved with duplicate UUIDs, can use the mod to clear the warning.

Who it’s for: Server owners who see repeated duplicate UUID messages in the console. Players need nothing installed.

Questions

Does DEUF have to be installed on the client?

No. It runs on the server alone, so players need nothing extra to join.

Which game versions does DEUF support?

Files cover 1.21.1 – 26.1 on NeoForge, with 12 release versions in total. The latest file is 26.1-1.0 for 26.1, published 2026-03-24.

Does the mod remove the log message for every entity?

It removes the message for entities whose UUID conflicts. The fix applies per entity once its chunk has loaded with the mod present.

In the catalog

DEUF - Duplicate Entity UUID Fix [NeoForge] is one of 3,545 Optimization mods on ModsFinder, and one of 1,250 Optimization mods for NeoForge. 11,959 mods support Minecraft 26.1.

Optimization mods3,545NeoForge modsMods for 26.111,959

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What the author says

"Keeping entity minecraft:xxxx that already exists with UUID xxxx" Now that message can occur quite often in case you use an old world. And there is no fix for it currently even though the bug is listed in the bug tracker for some time now. The logs (and server console, in case you have one - like me) also get…
KreloX, on the Modrinth page

Official listing

Owner
KreloX
Published
2026-03-05
Updated on Modrinth
2026-03-24
Facts verified
2026-10-15

Tags

CursedOptimizationUtility
Open on ModrinthCompare