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name: multiversion-support description: Guide for multi-version Minecraft mod development (1.20.1 + 1.21.1)

Multi-Version Support

Purpose: Guide for multi-version Minecraft mod development supporting 1.20.1 + 1.21.1 in a single codebase.

How it works: This skill is automatically activated when you mention tasks related to:

• Building for specific Minecraft versions
• Running the client for version testing
• Handling version-specific API differences
• Managing version-specific data packs
• Troubleshooting multi-version compatibility issues

Simply describe what you want to do, and Claude will reference the appropriate guidance from this skill.

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Overview

Documentation: Detailed migration plan is available in docs/multiversion_migration_plan.md.

Supported Versions: Minecraft 1.20.1 + 1.21.1 (single codebase)

Strategy:

• Custom Gradle scripts + abstraction layer approach (no external preprocessor dependencies)
• All code consolidated in one place (prioritizing AI development efficiency, avoiding Git branch separation)
• Status: ✅ Phase 1-6 completed (integration testing complete, 2026-01-11)

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Key Components

1. Data Pack Version Switching

Version-specific directories (resources-1.20.1/, resources-1.21.1/) switched via Gradle:

1.20.1:

• Plural folders: advancements/, loot_tables/, recipes/
• pack_format: 18

1.21.1:

• Singular folders: advancement/, loot_table/, recipe/
• pack_format: 48

2. Java Code Compatibility Layer

compat/ package absorbs API differences:

ItemStack:

• 1.20.1: NBT-based data storage
• 1.21.1: DataComponents system

SavedData:

• 1.20.1: No HolderLookup.Provider parameter
• 1.21.1: Requires HolderLookup.Provider parameter

ArmorMaterial:

• 1.20.1: Interface implementation
• 1.21.1: Record class

Tier:

• 1.20.1: getLevel() method available
• 1.21.1: getLevel() method removed

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Build Commands

Build for Specific Versions

Copy# Build for Minecraft 1.20.1
./gradlew build1_20_1

# Build for Minecraft 1.21.1 (default)
./gradlew build1_21_1

# Build all versions sequentially
./gradlew buildAll

# Explicit version build
./gradlew build -Ptarget_mc_version=1.20.1

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Run Client Commands

Auto-generated from gradle/subproject-run-tasks.gradle:

Fabric

Copy# Run Fabric client for 1.20.1
./gradlew fabric:runClient1_20_1

# Run Fabric client for 1.21.1
./gradlew fabric:runClient1_21_1

NeoForge/Forge

Copy# Run NeoForge/Forge client for 1.20.1
./gradlew neoforge:runClient1_20_1

# Run NeoForge client for 1.21.1
./gradlew neoforge:runClient1_21_1

Alternative Method (Explicit Version)

Copy# Fabric with explicit version
./gradlew :fabric:runClient -Ptarget_mc_version=1.20.1

# NeoForge with explicit version
./gradlew :neoforge:runClient -Ptarget_mc_version=1.21.1

Adding New Versions

Edit supportedVersions list in gradle/subproject-run-tasks.gradle

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Output JARs

Naming Convention:

• Fabric: chronodawn-{version}+{mc_version}-fabric.jar
• NeoForge: chronodawn-{version}+{mc_version}-neoforge.jar
• Example: chronodawn-0.3.0-beta+1.21.1-fabric.jar

Important Note:

• 1.20.1 is Fabric-only (NeoForge only supports 1.20.5+)

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Development Guidelines

When Writing Version-Specific Code

1. Check API Compatibility: Always verify if the API exists in both versions
2. Use Compat Layer: Add version-specific logic to compat/ package
3. Avoid Direct Version Checks: Use abstraction instead of if (version == "1.20.1")
4. Test Both Versions: Run ./gradlew buildAll before committing

Common Pitfalls

1. Hardcoding Data Pack Paths: Use Gradle-switched directories
2. Assuming API Availability: Check Minecraft version before using new APIs
3. Forgetting Compat Implementations: Always implement both version variants
4. Not Testing Both Versions: Always test both 1.20.1 and 1.21.1 builds

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Troubleshooting

Build Fails for Specific Version

Symptom: Build succeeds for one version but fails for another

Common Causes:

1. Using API that doesn't exist in older version
2. Missing compat layer implementation
3. Incorrect data pack structure for version

Solution: Check error message for missing class/method, add compat layer

Wrong Data Pack Format

Symptom: Resources not loading in-game

Checklist:

1. Verify pack_format matches Minecraft version (18 for 1.20.1, 48 for 1.21.1)
2. Check folder names (plural vs singular)
3. Confirm Gradle switched correct resource directory

Compat Layer Not Working

Symptom: Version-specific code fails at runtime

Solution:

1. Verify compat interface is properly implemented for both versions
2. Check factory method returns correct implementation
3. Confirm build includes correct compat classes

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Last Updated: 2026-01-16 Maintained by: Chrono Dawn Development Team