Preloading Tricks

Overview

Preloading Tricks is a developer-only mod that enables advanced operations during the very early stage of the mod loader.
It provides early hooks, Java Instrumentation-based class transformation, and SPI-driven callbacks for loader extension.

Supported environments:

• 1.20.1 – Forge & Fabric
• 1.21.x – NeoForge & Fabric

You can test on more version since it depends on the loader version instead of Minecraft version

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Features

• Early loader entrypoint via PreloadingEntrypoint (SPI-based)

  • Register callbacks using PreloadingTricksCallbacks events:
    • SETUP_LANGUAGE_ADAPTER – early language adapter setup stage
    • COLLECT_MOD_CANDIDATES – dynamically add mod candidate paths before discovery
    • SETUP_MODS – modify mod list (add/remove/query via ModManager API)

• Instrumentation-powered ClassTransform
  Can transform already-loaded classes, including Java core and classloader classes.

  • Forge-like (Forge/NeoForge): Configure via MANIFEST.MF (see below)
  • Fabric: Use AsmFabricLoader entrypoint

• Forge variant detection (Forge-like only)

  • Access ForgeVariants to detect specific Forge/NeoForge versions at runtime

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ClassTransform Configuration (Forge-like only)

For Forge/NeoForge, add the following attribute to your MANIFEST.MF:

ClassTransformConfig: xxxx.classtransform.json

Example config (xxxx.classtransform.json):

{
  "package": "settingdust.preloading_tricks.neoforge.transformer",
  "transformers": [
    "mod_setup_hook.FMLLoaderTransformer"
  ]
}

For Fabric, use AsmFabricLoader entrypoint instead.

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Forge Variant Detection (Forge-like only)

Allows a mod to load only on a specific Forge-like loader variant. This enables bundling both LexForge and NeoForge JARs together via jar-in-jar in a single mod file.

Configuration:

Specify your mod's target variant in MANIFEST.MF:

ForgeVariant: LexForge

or

ForgeVariant: NeoForge

Mods with a ForgeVariant specified will only load when running on the matching loader variant, allowing safe coexistence of variant-specific implementations.

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For developers who need to reach into the earliest moments of Minecraft’s loading process.