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Kotlin for Forge Mod Wiki & Guide

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A compatibility library that enables Minecraft mods written in the Kotlin programming language to run on the Forge mod loader.

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Contents (5)
  1. Overview
  2. Guides
  3. Frequently asked questions
  4. Gallery
  5. You May Also Like

Overview

Kotlin for Forge (KFF) serves as a bridge between the Kotlin programming language and the Minecraft Forge modding platform. While standard Forge is built for Java, KFF allows developers to leverage Kotlin's modern features—such as concise syntax, null safety, coroutines, and serialization—without requiring end-users to manually install separate language libraries.

As a library mod, Kotlin for Forge does not add gameplay elements like mobs, blocks, or biomes. Instead, it provides the underlying infrastructure and technical utilities necessary for other mods written in Kotlin to function correctly within the game.

Guides

Step-by-step, in-game.

Fixing a Crash Caused by a Missing Kotlin for Forge DependencyIdentifying the Crash A missing Kotlin for Forge dependency typically produces a startup crash with a message about…How to Check If a Mod Requires Kotlin for ForgeReading the Mod's Dependencies When a mod fails to load or crashes on startup, the culprit is often a missing Kotlin…Making Kotlin-Based Mods Work Together Without ConflictsWhy Conflicts Happen Multiple mods can all depend on Kotlin for Forge at the same time, and that is normal. Problems…Updating Kotlin for Forge Safely Without Breaking Your ModpackBefore You Update Back up your world and your mods folder before changing anything. Note which mods depend on Kotlin…

Frequently asked questions

What does Kotlin for Forge actually do?
It bundles the Kotlin runtime and language libraries so that mods written in Kotlin can load and run on Forge. Without it, any Kotlin-based mod will fail to start or crash on launch.
Do I need to install Kotlin for Forge if I don't have any Kotlin mods?
No, it does nothing on its own and only matters when another mod depends on it. If no mod requires it, you can leave it out.
How do I know which of my mods needs Kotlin for Forge?
Check the crash log or the mod list for a missing dependency error naming Kotlin for Forge. The mod that triggered it is the one that requires it.
My game crashes on startup saying Kotlin for Forge is missing. What do I do?
Add Kotlin for Forge to your modpack alongside the mod that needs it, and make sure both are for the same Minecraft version. The crash log will name the mod that's asking for it.

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