---
title: Mod Loaders
description: Fabric and Forge installation and management
---

# Mod Loaders

DropOut supports the two most popular Minecraft mod loaders: Fabric and Forge. Both can be easily installed and managed directly from the launcher.

## Fabric Support

### Overview

Fabric is a lightweight, modular modding toolchain focused on:
- Fast updates to new Minecraft versions
- Clean, minimal API
- Strong developer community
- Excellent performance

### Installation

1. Navigate to **Versions** tab
2. Click **"Install Fabric"**
3. Select Minecraft version
4. Choose Fabric loader version
5. Click **"Install"**
6. Wait for installation to complete

### How It Works

DropOut integrates with the Fabric Meta API to automatically fetch compatible loader versions. In the background, it generates the version JSON, handles library dependencies, and utilizes the inheritance system to ensure perfect compatibility with vanilla Minecraft. Detailed JSON structure can be found in [Technical Details](/docs/development/implementation#fabric-integration).

### Fabric Versions

**Loader Versions:**
- Latest stable (recommended)
- Specific versions for compatibility
- Beta/snapshot versions

**Game Versions:**
- All Minecraft versions from 1.14+
- Snapshots supported
- Combat Test versions

### Library Management

Fabric's dependencies are typically hosted on its official Maven repository. DropOut automatically resolves and downloads all required library files.

### Fabric API

Fabric Loader ≠ Fabric API:
- **Fabric Loader**: Mod loader (installed by DropOut)
- **Fabric API**: Library mod (download separately)

Many mods require Fabric API:
1. Download from [Modrinth](https://modrinth.com/mod/fabric-api) or [CurseForge](https://www.curseforge.com/minecraft/mc-mods/fabric-api)
2. Place in instance's `mods/` folder

## Forge Support

### Overview

Forge is the original and most popular Minecraft mod loader:
- Extensive mod ecosystem
- Mature API
- Wide version support
- Large community

### Installation

1. Navigate to **Versions** tab
2. Click **"Install Forge"**
3. Select Minecraft version
4. Choose Forge version
5. Click **"Install"**
6. Wait for installer to run
7. Installation complete

### How It Works

**Forge Installer:**
```rust
// Download Forge installer
let installer_url = format!(
    "https://maven.minecraftforge.net/net/minecraftforge/forge/{}/forge-{}-installer.jar",
    full_version, full_version
);

// Run installer
java -jar forge-installer.jar --installClient
```

**Profile Parsing:**
1. Forge installer creates version JSON
2. DropOut parses install profile
3. Extracts library dependencies
4. Processes processors (if any)
5. Generates launcher profile

**Version Format:**
```json
{
  "id": "1.20.4-forge-49.0.26",
  "inheritsFrom": "1.20.4",
  "mainClass": "cpw.mods.bootstraplauncher.BootstrapLauncher",
  "libraries": [...]
}
```

### Forge Versions

**Release Types:**
- **Latest**: Most recent stable
- **Recommended**: Most stable for production
- **Specific**: Version-locked for compatibility

**Minecraft Version Support:**
- Legacy versions (1.6.4+)
- Modern versions (1.13+)
- Latest versions (1.20+)

### Library Management

Forge's runtime depends on a significant number of library files, including its underlying `fmlloader` and bytecode manipulation libraries. DropOut automatically resolves the complex dependency tree and retrieves these files from both the official Forge Maven repository and Minecraft's official libraries.

For detailed analysis logic of Forge libraries, refer to [Implementation Details: Forge Core Library Resolution](../development/implementation.mdx#core-library-resolution).

### Forge Processors

Some Forge versions run "processors" during installation:
- Bytecode manipulation
- Library patching
- Mapping generation

DropOut handles these automatically.

## Version Inheritance

Both Fabric and Forge utilize Minecraft's version inheritance mechanism. In this model, the mod loader's version JSON only contains incremental changes relative to the vanilla version, addressed recursively upwards via the `inheritsFrom` field.

DropOut's launch engine automatically handles this complex merging of libraries, arguments, and assets. Detailed merging logic and code implementation can be viewed in [Implementation Details: Version Merging](../development/implementation.mdx#version-merging-mechanism).

## Comparison

| Feature | Fabric | Forge |
|---------|--------|-------|
| **Performance** | Excellent | Good |
| **Update Speed** | Very Fast | Moderate |
| **Mod Selection** | Growing | Extensive |
| **API Simplicity** | Simple | Complex |
| **Version Support** | 1.14+ | 1.6.4+ |
| **Developer Friendly** | Very | Moderate |
| **Stability** | Excellent | Excellent |

## Installing Mods

### Fabric Mods

1. Create/select instance
2. Ensure Fabric is installed
3. Download mods from:
   - [Modrinth](https://modrinth.com/)
   - [CurseForge](https://www.curseforge.com/)
   - [GitHub Releases](https://github.com/)
4. Place `.jar` files in `instances/<name>/mods/`
5. Launch game

**Compatibility:**
- Check Minecraft version
- Check Fabric Loader version
- Check for Fabric API requirement
- Read mod dependencies

### Forge Mods

1. Create/select instance
2. Ensure Forge is installed
3. Download mods from:
   - [CurseForge](https://www.curseforge.com/)
   - [Modrinth](https://modrinth.com/)
4. Place `.jar` files in `instances/<name>/mods/`
5. Launch game

**Compatibility:**
- Check Minecraft version exactly
- Check Forge version range
- Read mod dependencies
- Check for conflicts

## Troubleshooting

### Fabric Issues

**"Fabric Loader not found"**
- Reinstall Fabric
- Check version JSON exists
- Verify libraries downloaded

**"Mixin apply failed"**
- Mod incompatibility
- Remove conflicting mods
- Update Fabric Loader

**"Fabric API required"**
- Download Fabric API
- Match Minecraft version
- Place in mods folder

### Forge Issues

**"Forge installer failed"**
- Verify Java installation
- Check disk space
- Try older Forge version
- Check logs for details

**"Missing dependencies"**
- Install required mods
- Check mod version compatibility
- Read error message carefully

**"Class not found"**
- Forge version mismatch
- Reinstall Forge
- Verify libraries downloaded

### General Mod Issues

**Crash on Launch:**
1. Check crash report
2. Identify problematic mod
3. Remove or update mod
4. Test with minimal mods
5. Add mods back incrementally

**Performance Problems:**
1. Too many mods installed
2. Increase memory allocation
3. Install performance mods:
   - Fabric: Sodium, Lithium
   - Forge: OptiFine, Magnesium
4. Remove resource-heavy mods

## API Reference

### Tauri Commands

**Install Fabric:**
```typescript
await invoke('install_fabric', {
  minecraftVersion: '1.20.4',
  loaderVersion: '0.15.0'
});
```

**Install Forge:**
```typescript
await invoke('install_forge', {
  minecraftVersion: '1.20.4',
  forgeVersion: '49.0.26'
});
```

**List Fabric Versions:**
```typescript
const versions = await invoke('get_fabric_versions', {
  minecraftVersion: '1.20.4'
});
```

**List Forge Versions:**
```typescript
const versions = await invoke('get_forge_versions', {
  minecraftVersion: '1.20.4'
});
```

### Events

**Installation Progress:**
```typescript
listen('mod-loader-progress', (event) => {
  const { stage, percent } = event.payload;
  // Stages: "downloading", "installing", "processing", "complete"
});
```

## Best Practices

### For Players

1. **Choose one mod loader** per instance
2. **Match versions exactly** - Minecraft and loader
3. **Read mod requirements** before installing
4. **Start small** - Add mods incrementally
5. **Backup worlds** before adding mods
6. **Check compatibility** lists
7. **Update cautiously** - Test in separate instance

### For Modpack Creators

1. **Document versions** - MC, loader, all mods
2. **Test thoroughly** - All features
3. **List dependencies** - Including API
4. **Provide changelog** - For updates
5. **Version lock** - For stability
6. **Include configs** - Pre-configured
7. **Test updates** - Before release

## Future Features

- **Mod browser** - Install mods from launcher
- **Automatic updates** - Keep mods current
- **Dependency resolution** - Auto-install requirements
- **Conflict detection** - Warn about incompatibilities
- **Profile export** - Share modpack configurations
- **CurseForge integration** - Direct modpack import
- **Modrinth integration** - Mod search and install
