Yarn to Mojang names

Checked against Fabric’s documentation and blog on 2 November 2026.

Why you have to switch

Until 1.21.11, Minecraft’s code was obfuscated. Fabric mods used one of two name sets to make it readable: Yarn, Fabric’s community names (CreeperEntity), or Mojang’s names, the official ones (Creeper). Under both, compiled mods used Intermediary names (class_1548) so they kept working across versions.

From 26.1 the game ships with Mojang’s names in the code itself. Fabric stopped maintaining Yarn and says:

• Yarn is no longer officially supported (Fabric, 14 March 2026).
• Intermediary will no longer exist; the game uses Mojang’s names at runtime (Fabric, 31 October 2025).
• Mappings are not supported on 26.1, so migrate to Mojang names before you change the Minecraft version (Fabric docs).

Mojang announced the change in Removing obfuscation in Java Edition. If your mod already uses Mojang names (with or without Parchment), skip this page.

Two tools

Fabric’s Migrating Mappings page offers two:

Tool	What it is	Kotlin
Loom’s migrateMappings task	A Gradle task in Fabric’s Gradle plugin. Semi-automatic.	Not supported
Ravel	A plugin for IntelliJ IDEA with a dialog. Fabric says it may do better on complex projects because it uses the IDE to resolve changes.	Supported

Fabric API itself was migrated with Ravel. Fabric’s page is clear that neither tool is perfect: you review the result and fix things by hand, mixins most of all.

The steps with Loom

1. Stay on 1.21.11. Commit or back up.

2. Run migrateMappings with Mojang’s names for 1.21.11. Exact commands and options: Loom’s migrateMappings task.

3. In build.gradle, replace the Yarn line with Mojang’s names:

   dependencies {
       // was: mappings "net.fabricmc:yarn:${project.yarn_mappings}:v2"
       mappings loom.officialMojangMappings()
   }

4. Refresh Gradle and build.

5. Read through your code for mixin targets and anything that was not renamed. Fabric’s page names mappings.dev and Linkie as tools to learn the new names.

6. Only now start the 26.1 build changes. On 26.1 the mappings line goes away completely.

Fabric API names changed too

Fabric API used Yarn-style names before. On 26.1 they follow Mojang’s names, and the change is not backwards compatible: ItemGroupEvents is now CreativeModeTabEvents. Fabric lists every rename, with an IntelliJ IDEA migration map, in its Fabric API 26.1 porting guide.

In Linen

Linen has no mappings-migration button yet. Run migrateMappings from a terminal, or ask Claude Code to run it.

• Hovers show a name in Mojang, Yarn, intermediary and Parchment, where the version has them. Hover a Yarn name in your 1.21.11 code to see its Mojang name.
• Minecraft’s code and Find usages browse the decompiled game for the project’s version, on your machine.
• Linen Check reads names, mixins and the build after the change, and names the file and the fix.
• Claude Code, Anthropic’s extension, on your own Claude plan, gets Linen’s tools, including linen_mappings, lookup_symbol and gradle, and Linen Check after every edit. Ask it to go through what the migration missed.