Kotlin for Forge is a library mod that adds Kotlin programming language support to Minecraft Forge and NeoForge, allowing mod developers to write and run mods using Kotlin instead of Java.
Minecraft modding has traditionally been a Java-only affair, but a growing number of mod developers prefer Kotlin for its concise syntax, null safety, and coroutine support. The problem is that Forge does not natively understand Kotlin code. Kotlin for Forge bridges that gap by bundling the Kotlin runtime libraries and providing a custom language loader so Forge can recognize and load Kotlin-based mods. With over 27 million downloads on Modrinth, it has become one of the most widely used library mods in the entire Forge ecosystem — a testament to how many popular mods now depend on it. Created and maintained by thedarkcolour, the project has been actively updated since early 2021 and continues to ship new releases for the latest Minecraft versions.
Key Features of Kotlin for Forge
- Kotlin Language Loader (KotlinLanguageProvider) — This is the core reason the mod exists. It registers a custom language provider with Forge so that mods written in Kotlin can use
@Modobject declarations just like Java mods use class-based entry points. Without this loader, Forge would simply refuse to load any Kotlin mod. - Bundled Kotlin Runtime Libraries — Kotlin for Forge shades (embeds) the full Kotlin standard library, Kotlin coroutines, Kotlin JSON serialization, and JetBrains annotations directly into the mod JAR. This means players do not need to install Kotlin separately, and mod developers do not risk version conflicts between different Kotlin mods.
- AutoKotlinEventBusSubscriber — Forge uses an event bus system for mod lifecycle events. This feature automatically detects and registers
@EventBusSubscriberdeclarations written in Kotlin, saving developers from writing boilerplate registration code. For players, this translates to fewer bugs and more reliable mod behavior. - Custom IEventBus Implementation — Unlike the older Kottle library, Kotlin for Forge (since version 1.2.0) provides its own event bus implementation that supports
addListenerandaddGenericListenerwith Kotlin function references. This gives developers a more natural, Kotlin-idiomatic way to handle events, which leads to cleaner and more maintainable mod code. - Coroutine Support — By bundling Kotlin coroutines, the mod enables developers to write asynchronous code without the complexity of Java threading. Mods that perform background tasks like world scanning or data processing can use coroutines for smoother performance without blocking the main game thread.
- Standalone Library Usage — You do not have to use the language loader or any of the Kotlin-specific Forge features. Some developers install Kotlin for Forge purely to access the bundled Kotlin libraries in their otherwise Java-based projects, giving them flexibility in how they adopt Kotlin features.
- Dual Loader Support (Forge & NeoForge) — The mod ships builds for both Minecraft Forge and NeoForge across a wide range of Minecraft versions. Whether your modpack uses the classic Forge loader or the newer NeoForge fork, Kotlin for Forge has you covered.
How to Install Kotlin for Forge
- Install Minecraft Forge or NeoForge for your Minecraft version. Kotlin for Forge supports versions from 1.16.5 up to 1.21.11.
- Download the correct Kotlin for Forge file for your Minecraft version and loader from the download section below. Make sure the loader type (Forge or NeoForge) matches your installation.
- Open your Minecraft installation directory. On Windows, press Win + R, type
%appdata%\.minecraft, and press Enter. - Place the downloaded
.jarfile into themodsfolder. If the folder does not exist, create it. - Launch Minecraft using your Forge or NeoForge profile. Kotlin for Forge loads automatically in the background — there are no settings to configure and no in-game menus.
Requirements & Compatibility
| Requirement | Details |
|---|---|
| Mod Loader | Minecraft Forge or NeoForge |
| Minecraft Versions | 1.16.5, 1.17–1.17.1, 1.18–1.18.2, 1.19–1.19.4, 1.20–1.20.6, 1.21–1.21.11 |
| Latest Build | Kotlin for Forge 6.2.0 (March 2026) |
| License | LGPL-2.1-only (open source) |
| Kotlin Version (bundled) | Kotlin 1.4.21+, Coroutines 1.4.2+, JSON Serialization 1.0.1+ |
| Client/Server | Required on both sides if a dependent mod needs it |
What's New
- Updated to Kotlin for Forge 6.2.0 with support for Minecraft 1.21.11 and 1.21.10.
- Continued dual-loader support for both Forge and NeoForge on the latest Minecraft releases.
- Bundled Kotlin libraries kept up to date with upstream JetBrains releases.
- Ongoing compatibility fixes and improvements for newer Forge and NeoForge APIs.
Pros and Cons
Pros
- Essential dependency used by thousands of Kotlin-based mods
- Supports both Forge and NeoForge across 30 Minecraft versions
- Actively maintained since 2021 with frequent updates
- Bundles all required Kotlin libraries — no extra downloads needed
- Open source under LGPL-2.1, with full source code available on GitHub
- Appears to be lightweight with no noticeable performance overhead for players
Cons
- Adds no gameplay features — only useful as a dependency for other mods
- Not available for Fabric or Quilt (those loaders use a separate Kotlin adapter)
- Bundled Kotlin version may lag behind the latest JetBrains release
- Players may not realize they need it until a dependent mod fails to load
Alternatives to Kotlin for Forge
- Fabric Language Kotlin — The Fabric equivalent of Kotlin for Forge, providing Kotlin runtime and language support for Fabric-based mods.
- Forgelin — An older Kotlin language adapter for Forge that preceded Kotlin for Forge, primarily used with legacy Minecraft versions.
- Kottle — Another earlier Kotlin adapter for Forge that Kotlin for Forge was designed to replace, offering improved event bus support and broader compatibility.
Download Kotlin for Forge
| Minecraft Version | Forge | NeoForge |
|---|---|---|
| For Minecraft 1.21.11 | Download | Download |
| For Minecraft 1.21.10 | Download | Download |
| For Minecraft 1.21.9 | Download | Download |
| For Minecraft 1.21.8 | Download | Download |
| For Minecraft 1.21.7 | Download | Download |
| For Minecraft 1.21.6 | Download | Download |
| For Minecraft 1.21.5 | Download | Download |
| For Minecraft 1.21.4 | Download | Download |
| For Minecraft 1.21.3 | Download | Download |
| For Minecraft 1.21.2 | Download | Download |
| For Minecraft 1.21.1 | Download | Download |
| For Minecraft 1.21 | Download | Download |
Always download mods from official sources to stay safe.
Frequently Asked Questions
Do I need Kotlin for Forge if I am just a regular player?
Only if another mod requires it. Kotlin for Forge is a dependency library — it provides no gameplay features on its own. If you see an error message mentioning a missing Kotlin for Forge dependency when launching Minecraft, download and install it alongside the mod that needs it.
Is Kotlin for Forge compatible with NeoForge?
Yes — Kotlin for Forge ships dedicated builds for both Minecraft Forge and NeoForge. When downloading, make sure you select the file that matches your specific loader. Both versions are available for Minecraft 1.21.11 and many earlier releases.
Will Kotlin for Forge slow down my game?
No noticeable impact has been widely reported. The mod bundles Kotlin runtime libraries that load once during startup, and after that the libraries sit in memory like any other dependency. It does not run background processes or modify game rendering in any way.
What is the difference between Kotlin for Forge and Kottle?
Kotlin for Forge is the newer, actively maintained replacement. Since version 1.2.0, it includes its own IEventBus implementation that supports function references — a feature Kottle lacks. Kotlin for Forge also receives regular updates for the latest Minecraft versions, while Kottle has been largely abandoned.
Can I use Kotlin for Forge on Fabric or Quilt?
No — Kotlin for Forge is designed exclusively for Minecraft Forge and NeoForge. Fabric and Quilt users should install Fabric Language Kotlin instead, which serves the same purpose for those mod loaders.
