{"slug":"minecraft-modding-3","title":"minecraft-modding","summary":"Create, modify, debug, or migrate Minecraft mods for current NeoForge or Fabric 26.x, legacy 1.21.x, and Forge 1.20.1. Use for loader-based gameplay code and assets; use minecraft-multiloader when one codebase must target both modern loaders.","platform":"Codex CLI","tags":[],"authorName":"LLM Mart","authorSlug":"llm-mart","score":0,"source":"github","price":null,"verified":false,"createdAt":"2026-09-07T18:38:50.107521Z","repo":{"url":"https://github.com/Jahrome907/minecraft-agent-skills","stars":151,"forks":9,"license":"MIT","updatedAt":"2026-09-13T05:52:30Z"},"bodyHtml":"
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name: minecraft-modding\ndescription: \"Create, modify, debug, or migrate Minecraft mods for current NeoForge or Fabric 26.x, legacy 1.21.x, and Forge 1.20.1. Use for loader-based gameplay code and assets; use minecraft-multiloader when one codebase must target both modern loaders.\"

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Minecraft Modding Skill

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Overview

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This skill guides Codex through developing open-source Minecraft mods.\nTarget platforms:

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PlatformMC VersionJavaBuild System
NeoForge26.x current; 1.21.11 examples retainedJava 25 current; Java 21 on 1.21.xGradle + ModDevGradle
Forge1.20.1 legacy laneJava 17Gradle + ForgeGradle 6
Fabric26.x current; 1.21.11 examples retainedJava 25 current; Java 21 on 1.21.xGradle + Fabric Loom
Architectury (multiloader)26.x or 1.21.xMatch MinecraftGradle + Architectury Loom
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Always confirm the platform and Minecraft version from gradle.properties or build.gradle\nbefore writing any mod-specific code.

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Minecraft 26.1 introduced Java 25 and unobfuscated game executables. For 26.x\nprojects, start from the current loader generator or example mod and preserve\nits build layout. Do not copy the 1.21.11 mapping, Loom plugin, remapping task,\nor Java 21 snippets in this skill into a 26.x project. Fabric 26.x uses the\nnon-remapping Loom path and official names; NeoForge 26.x should start from the\ncurrent NeoForge generator. Treat the detailed API references here as the\nlegacy 1.21.x lane unless a section explicitly says 26.x.

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Routing Boundaries

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1. Identifying the Platform

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# NeoForge project signature\ngrep -r \"net.neoforged\" gradle.properties build.gradle settings.gradle 2>/dev/null | head -5\n\n# Forge 1.20.1 project signature\ngrep -r \"net.minecraftforge\" gradle.properties build.gradle settings.gradle 2>/dev/null | head -5\n\n# Fabric project signature\ngrep -r \"fabric\" gradle.properties build.gradle settings.gradle 2>/dev/null | head -5\n\n# Read mod ID and version\ncat gradle.properties\n
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Key files per platform:

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2. Build & Test Commands

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# Build the mod jar\n./gradlew build\n\n# Run the Minecraft client to test\n./gradlew runClient\n\n# Run a dedicated server to test\n./gradlew runServer\n\n# Run game tests (NeoForge JUnit-style game tests)\n./gradlew runGameTestServer\n\n# Run data generation (generates JSON assets automatically)\n./gradlew runData\n\n# Remove this project's generated build outputs before a fresh rebuild\n./gradlew clean\n\n# Check for dependency updates (optional)\n./gradlew dependencyUpdates\n
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./gradlew build runs the project's configured build tasks. Candidate mod jars are\nusually under build/libs/, but task names and file names are project-specific.\nTreat the build output as compilation evidence, then identify the intended\ndistributable before publishing it.

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3. Project Layout (NeoForge)

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src/\n  main/\n    java/<groupId>/<modid>/\n      MyMod.java               ← @Mod entry point\n      block/\n        ModBlocks.java         ← DeferredRegister.Blocks\n        MyCustomBlock.java\n      item/\n        ModItems.java          ← DeferredRegister.Items\n      entity/\n        ModEntities.java       ← DeferredRegister.Entities\n      menu/                    ← custom GUI containers\n      recipe/\n      worldgen/\n      datagen/\n        ModDataGen.java        ← GatherDataEvent handler\n        providers/\n    resources/\n      META-INF/\n        neoforge.mods.toml     ← mod metadata (renamed from mods.toml in NeoForge 1.20.5+)\n      assets/<modid>/\n        blockstates/           ← JSON blockstate definitions\n        models/\n          block/               ← block model JSON\n          item/                ← item model JSON\n        items/                 ← 1.21.x item-definition JSON\n        textures/\n          block/               ← 16×16 PNG textures\n          item/\n        lang/\n          en_us.json           ← translation strings\n      data/<modid>/\n        recipe/                ← crafting recipe JSON (26.x)\n        loot_table/\n          blocks/              ← per-block loot table JSON\n        tags/\n          blocks/\n          items/\n
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4. Project Layout (Forge 1.20.1)

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Use this layout only when minecraft_version=1.20.1 and the project depends on\nnet.minecraftforge:forge. Forge 1.20.1 is not NeoForge: keep mods.toml,\nnet.minecraftforge.* imports, Java 17, and ForgeGradle 6 patterns.

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src/\n  main/\n    java/<groupId>/<modid>/\n      MyMod.java               <- @Mod entry point\n      block/\n        ModBlocks.java         <- DeferredRegister.Blocks\n      item/\n        ModItems.java          <- DeferredRegister.Items\n      datagen/\n        ModDataGen.java        <- GatherDataEvent handler\n    resources/\n      META-INF/\n        mods.toml              <- Forge metadata\n      assets/<modid>/          <- client assets\n      data/<modid>/            <- server data using 1.20.1 paths\n
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See references/forge-1.20.1-api.md before editing Forge 1.20.1 projects.

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5. Project Layout (Fabric)

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src/\n  main/\n    java/<groupId>/<modid>/\n      MyMod.java               ← implements ModInitializer\n      client/\n        MyModClient.java       ← implements ClientModInitializer\n      block/\n      item/\n      mixin/                   ← Mixin classes\n    resources/\n      fabric.mod.json\n      assets/<modid>/          ← same as NeoForge\n      data/<modid>/            ← same as NeoForge\n      <modid>.mixins.json      ← mixin configuration\n
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6. Core Concepts Cheatsheet

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Sides

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Registries

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Everything in Minecraft lives in a registry. Always register objects; never\nconstruct them at field initializer time outside a registry call. Use the\nmapping-appropriate registry constants for the loader you are editing:

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TypeNeoForge / Mojang mappingsFabric / Yarn mappings
BlocksBuiltInRegistries.BLOCKRegistries.BLOCK
ItemsBuiltInRegistries.ITEMRegistries.ITEM
Entity typesBuiltInRegistries.ENTITY_TYPERegistries.ENTITY_TYPE
Block entity typesBuiltInRegistries.BLOCK_ENTITY_TYPERegistries.BLOCK_ENTITY_TYPE
Menu / screen-handler typesBuiltInRegistries.MENURegistries.SCREEN_HANDLER
Sound eventsBuiltInRegistries.SOUND_EVENTRegistries.SOUND_EVENT
BiomesRegistries.BIOME registry keysRegistryKeys.BIOME registry keys
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Do not copy older Registry.BLOCK / Registry.ITEM constants into 1.21.x code;\nthose names are stale for the examples in this skill.

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ResourceLocation / Identifier

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Every registry entry needs a namespaced ID:

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// NeoForge / vanilla Java\nResourceLocation id = ResourceLocation.fromNamespaceAndPath(\"mymod\", \"my_block\");\n\n// Fabric with Yarn mappings\nIdentifier id = Identifier.of(\"mymod\", \"my_block\");\n
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7. NeoForge Quick Patterns (26.x)

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For 26.x, use the explicitly labelled 26.x sections in\nreferences/common-patterns.md and select the project's exact version in the\nNeoForge documentation.\nreferences/neoforge-api.md contains legacy 1.21.x / Java 21 patterns only;\ndo not copy its dependency pins into a 26.x project.

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// Main mod class\n@Mod(MyMod.MOD_ID)\npublic class MyMod {\n    public static final String MOD_ID = \"mymod\";\n\n    public MyMod(IEventBus modEventBus) {\n        ModBlocks.BLOCKS.register(modEventBus);\n        ModItems.ITEMS.register(modEventBus);\n        modEventBus.addListener(this::commonSetup);\n    }\n\n    private void commonSetup(FMLCommonSetupEvent event) {\n        // runs after all mods are registered\n    }\n}\n
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// Block registration\npublic class ModBlocks {\n    public static final DeferredRegister.Blocks BLOCKS =\n        DeferredRegister.createBlocks(MyMod.MOD_ID);\n\n    public static final DeferredBlock<Block> MY_BLOCK =\n        BLOCKS.registerSimpleBlock(\"my_block\",\n            BlockBehaviour.Properties.of()\n                .mapColor(MapColor.STONE)\n                .strength(1.5f, 6.0f)\n                .sound(SoundType.STONE)\n                .requiresCorrectToolForDrops());\n}\n
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8. Forge 1.20.1 Quick Patterns

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See full patterns in references/forge-1.20.1-api.md.

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// Main mod class\n@Mod(MyMod.MOD_ID)\npublic class MyMod {\n    public static final String MOD_ID = \"mymod\";\n\n    public MyMod(FMLJavaModLoadingContext context) {\n        IEventBus modEventBus = context.getModEventBus();\n        ModBlocks.BLOCKS.register(modEventBus);\n        ModItems.ITEMS.register(modEventBus);\n        modEventBus.addListener(this::commonSetup);\n        MinecraftForge.EVENT_BUS.register(this);\n    }\n\n    private void commonSetup(FMLCommonSetupEvent event) {\n        // runs after registries are prepared\n    }\n}\n
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// Block registration\npublic class ModBlocks {\n    public static final DeferredRegister<Block> BLOCKS =\n        DeferredRegister.create(ForgeRegistries.BLOCKS, MyMod.MOD_ID);\n\n    public static final RegistryObject<Block> MY_BLOCK =\n        BLOCKS.register(\"my_block\", () -> new Block(\n            BlockBehaviour.Properties.of()\n                .mapColor(MapColor.STONE)\n                .strength(1.5f, 6.0f)\n                .sound(SoundType.STONE)\n                .requiresCorrectToolForDrops()));\n}\n
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9. Fabric Quick Patterns

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Match the project's Minecraft version and mappings in the\nFabric documentation.\nreferences/fabric-api.md contains legacy 1.21.x / Java 21 patterns only.\nThe explicitly labelled 26.x sections in references/common-patterns.md\nuse NeoForge syntax; adapt them against the exact Fabric API rather than\ncopying loader-specific classes or legacy dependency pins.

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// Main mod class\npublic class MyMod implements ModInitializer {\n    public static final String MOD_ID = \"mymod\";\n    public static final Logger LOGGER = LoggerFactory.getLogger(MOD_ID);\n\n    @Override\n    public void onInitialize() {\n        ModBlocks.initialize();\n        ModItems.register();\n    }\n}\n
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// Fabric 26.x with official Mojang mappings. Create the key before the object\n// so its properties receive the required id during construction.\npublic final class ModBlocks {\n    public static final ResourceKey<Block> MY_BLOCK_KEY = ResourceKey.create(\n        Registries.BLOCK,\n        Identifier.fromNamespaceAndPath(MyMod.MOD_ID, \"my_block\")\n    );\n\n    public static final Block MY_BLOCK = register(\n        MY_BLOCK_KEY,\n        Block::new,\n        BlockBehaviour.Properties.of()\n            .mapColor(MapColor.STONE)\n            .strength(1.5f, 6.0f)\n            .sound(SoundType.STONE)\n            .requiresCorrectToolForDrops()\n    );\n\n    private static Block register(ResourceKey<Block> key,\n            Function<BlockBehaviour.Properties, Block> factory,\n            BlockBehaviour.Properties properties) {\n        Block block = factory.apply(properties.setId(key));\n        return Registry.register(BuiltInRegistries.BLOCK, key, block);\n    }\n\n    public static void initialize() {}\n}\n
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Call ModBlocks.initialize() from the Fabric initializer. The Yarn-named\n1.21.11 examples remain in references/fabric-api.md; do not mix those names\nwith this 26.x pattern.

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10. JSON Asset Templates

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Always provide matching JSON assets for every registered block/item.\nCodex should generate or update these files alongside Java code.\nFor Forge 1.20.1, check references/forge-1.20.1-api.md for legacy server-data\ndirectory names before creating loot tables or tags.

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See references/common-patterns.md for full JSON templates for:

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11. Data Generation

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Prefer data generation over hand-authored JSON for maintainability.

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// NeoForge – register data gen providers in GatherDataEvent\n@SubscribeEvent\npublic static void gatherData(GatherDataEvent event) {\n    DataGenerator gen = event.getGenerator();\n    PackOutput output = gen.getPackOutput();\n    ExistingFileHelper helper = event.getExistingFileHelper();\n    CompletableFuture<HolderLookup.Provider> lookupProvider = event.getLookupProvider();\n\n    gen.addProvider(event.includeClient(), new ModBlockStateProvider(output, helper));\n    gen.addProvider(event.includeClient(), new ModItemModelProvider(output, helper));\n    gen.addProvider(event.includeServer(), new ModRecipeProvider(output, lookupProvider));\n    gen.addProvider(event.includeServer(), new ModLootTableProvider(output, lookupProvider));\n    gen.addProvider(event.includeServer(), new ModBlockTagsProvider(output, lookupProvider, helper));\n}\n
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Run data generation with ./gradlew runData, then commit the generated files.\nFor Forge 1.20.1, use the mod-event-bus registration, GatherDataEvent\nsignature, provider classes, and legacy output paths from\nreferences/forge-1.20.1-api.md.

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12. Common Tasks Checklist

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When adding a new block:

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When adding a new item:

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When adding a new entity:

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13. Open-Source Conventions

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14. References

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