Project setup

fabric.mod.json

Every addon describes itself in a normal Fabric fabric.mod.json:

{
  "schemaVersion": 1,
  "id": "my-addon",
  "version": "${version}",
  "name": "My Addon",
  "description": "What your addon does, in one sentence.",
  "authors": ["You"],
  "license": "MIT",
  "icon": "assets/my-addon/icon.png",
  "environment": "client",
  "entrypoints": { "lynx": ["com.example.myaddon.MyAddon"] },
  "custom": {
    "lynx": {
      "api": 1,
      "minecraft": ["1.21.1", "26.3"],
      "depends": { "other-addon": ">=1.2.0" }
    }
  }
}

Field	Required	Meaning
id	yes	Unique id, a-z 0-9 - _. In the store it belongs to the account that submits it first.
entrypoints.lynx	yes	Exactly one class that implements LynxAddon
custom.lynx.api	yes	API major version the addon was written for, currently 1
custom.lynx.minecraft	no	Only these Minecraft versions. Leave it out for all.
custom.lynx.depends	no	Other addons with a version range (>=1.2.0, 1.x, *)
name, description, authors, license, icon	no	Shown in the mod menu and the store

Dependencies on other addons

Use custom.lynx.depends, not Fabric's own depends. If something from Fabric's depends is missing, the whole game refuses to start. With custom.lynx.depends only your addon is switched off, and the mod menu shows why. Addons are loaded in dependency order.

The entry point

public final class MyAddon implements LynxAddon {
    @Override
    public void onLoad(LynxApi lynx) {
        lynx.modules().register(new HelloWidget());
    }

    @Override
    public void onShutdown() {
        // optional: when the game closes. Module settings are saved by LynxClient.
    }
}

onLoad runs once at start, after LynxClient's own modules and after the addons yours depends on. If it throws, the addon is marked as failed, the modules it registered are removed again and the game keeps running.

LynxApi gives you:

Method
modules()	Register and look up modules
events()	The event bus
game()	Read-only game state
addons()	All addons found at start, with their state
version() / minecraftVersion()	LynxClient version, running Minecraft version

Outside onLoad you can get the same object with Lynx.api().

Gradle

plugins { java }

version = "1.0.0"

repositories { maven("https://download.lynxclient.de/maven") }
dependencies { compileOnly("net.lynxclient:lynx-api:0.1.17") }

tasks.withType<JavaCompile>().configureEach {
    options.release = 17
    options.encoding = "UTF-8"
}

tasks.processResources {
    inputs.property("version", project.version)
    filesMatching("fabric.mod.json") { expand("version" to project.version) }
}

Libraries other than the Lynx API cannot be used in store addons yet, because the store builds your addon against the API only.