Fabric

The fabric plugin, from @opys/minecraft.

Fabric, for any Minecraft version Fabric supports.

// opys.config.mjs
export default defineConfig({
  plugins: [
    fabric({ version: '1.21.4' }),
    java({ version: '21' }),
  ],
  manifest: {
    command: '@fabric.command',
    args: [
      '@fabric.jvmArgs',
      '@fabric.mainClass',
      '@fabric.gameArgs',
    ],
    workdir: '${game_directory}',
  },
});

Use it instead of minecraft. A loader brings the game with it.

Options

Option	What it does
version	Which build. See below.
loader	A Fabric loader version. Left out: the newest stable one.
source	A mirror of Fabric Meta.
manifestBase	A mirror of Mojang's version list.
libraries	Libraries to add or replace.

version

A plain Minecraft version. Fabric has no aliases.

fabric({ version: '1.21.4' }); // the newest stable Fabric loader
fabric({ version: '1.21.4', loader: '0.16.10' }); // a pinned one

Without loader, the newest stable loader is used, so it can change between builds. Pin it for a pack that never moves.

What it adds

Everything Vanilla Minecraft adds, with these differences.

Kind	What
Files	The Fabric loader and its libraries, on top of the game's.
Launch	command, jvmArgs, mainClass, gameArgs.
Variables	The same as vanilla.
Environment	None.

Each one below: what it is, and how it ends up in the manifest.

Files · Fabric libraries

The Fabric loader and what it needs, from Fabric's server.

// opys.config.mjs
export default defineConfig({
  plugins: [
    fabric({ version: '1.21.4' }),
    java({ version: '21' }),
  ],
  manifest: {
    command: '@fabric.command',
    args: [
      '@fabric.jvmArgs',
      '@fabric.mainClass',
      '@fabric.gameArgs',
    ],
    workdir: '${game_directory}',
  },
});

// in the manifest
{
  "path": "${library_directory}/net/fabricmc/fabric-loader/0.19.5/fabric-loader-0.19.5.jar",
  "source": { "url": "https://maven.fabricmc.net/net/fabricmc/fabric-loader/0.19.5/fabric-loader-0.19.5.jar" }
}

Launch

The vanilla command line with Fabric's main class, and one line telling Fabric which class the real game is.

// opys.config.mjs
export default defineConfig({
  plugins: [
    fabric({ version: '1.21.4' }),
    java({ version: '21' }),
  ],
  manifest: {
    command: '@fabric.command',
    args: [
      '@fabric.jvmArgs',
      '@fabric.mainClass',
      '@fabric.gameArgs',
    ],
    workdir: '${game_directory}',
  },
});

// in the manifest
"launch": {
  // '@fabric.command'
  "command": "${java_bin}",
  "args": [
    // '@fabric.jvmArgs'
    // … the vanilla JVM arguments, then:
    "-cp",
    "${classpath}",
    "-DFabricMcEmu= net.minecraft.client.main.Main ",
    // '@fabric.mainClass'
    "net.fabricmc.loader.impl.launch.knot.KnotClient",
    // '@fabric.gameArgs'
    "--username", "${auth_player_name}",
    "--version", "${version_name}"
    // … the vanilla game arguments
  ],
  "workdir": "${game_directory}"
}

You write	Becomes
'@fabric.command'	The program to run: whatever Java the pack has.
'@fabric.jvmArgs'	Arguments for Java itself, ending with the classpath.
'@fabric.mainClass'	The class to start. One argument.
'@fabric.gameArgs'	Arguments for the game: who is playing, and where things are.

Variables

The same names as vanilla. classpath now has this loader's libraries ahead of the game's.

// opys.config.mjs
export default defineConfig({
  plugins: [
    fabric({ version: '1.21.4' }),
    java({ version: '21' }),
  ],
  manifest: {
    command: '@fabric.command',
    args: [
      '@fabric.jvmArgs',
      '@fabric.mainClass',
      '@fabric.gameArgs',
    ],
    workdir: '${game_directory}',
  },
});

// in the manifest
"vars": {
  "game_directory": "${root}/",
  "library_directory": "${root}/libraries",
  // … the rest, as in vanilla
}

Nothing runs on the player's machine before the game. Fabric has no install step.

Good to know

• Pair it with java({ version: '21' }).