mc-modpack-mcp

MCP (Model Context Protocol) server for Minecraft modpack diagnostics. Supports Fabric/Forge mod conflict detection, log analysis, crash reports, and dependency lookup. get_java_versions requires PCL launcher on Windows; all other tools work cross-platform.

Features

• Java version detection — reads PCL config to list all available Java runtimes

• Version info — parses instance JSON to extract Minecraft version, loader, Java requirements, JVM args

• Conflict detection — finds known problematic mod combinations (renderers, UI libs, JEI, Fabric API)

• Cleanliness scan — detects non-JAR files, source jars, scripts in mods/ directory

• Log analysis — reads latest.log with level filtering (INFO/WARN/ERROR) and keyword search

• Crash report analysis — finds and parses crash-reports, extracts exception type and summary

• Dependency lookup — queries Modrinth API for mod version and dependency info

Related MCP server: mcdev-mcp

Tools

Installation

Prerequisites

• Node.js 18+

• npm

• A Minecraft instance (any launcher — macOS/Linux users must pass mc_dir explicitly for all tools)

Note: get_java_versions reads PCL launcher config and works on Windows only. All other tools are cross-platform.

Build

cd mc-modpack-mcp
npm install
npm run build

Run as standalone MCP server

node dist/index.js

The server communicates via stdio (JSON-RPC 2.0). It can be consumed by any MCP-compatible client.

Configuration for MCP clients

Add to your MCP client config (e.g., .mcp.json or equivalent):

{
  "mcpServers": {
    "mc-modpack": {
      "command": "node",
      "args": ["/absolute/path/to/mc-modpack-mcp/dist/index.js"]
    }
  }
}

Usage Examples

Get Java versions from PCL

{
  "name": "get_java_versions",
  "arguments": {
    "mc_dir": "{your_minecraft_directory}"
  }
}

Detect conflicts in an instance

{
  "name": "detect_conflicts",
  "arguments": {
    "mc_dir": "{your_minecraft_directory}",
    "instance_id": "rpg"
  }
}

Read WARN logs (last 50 lines)

{
  "name": "read_log",
  "arguments": {
    "mc_dir": "{your_minecraft_directory}",
    "instance_id": "rpg",
    "level": "WARN",
    "tail": 50
  }
}

Check mod dependencies via Modrinth

{
  "name": "check_mod_dependencies",
  "arguments": {
    "project_id": "sodium",
    "mc_version": "1.20.1",
    "loader": "fabric"
  }
}

Architecture

mc-modpack-mcp/
├── src/
│   └── index.ts        # All tool implementations + MCP server setup
├── dist/               # Compiled JavaScript (output of tsc)
├── skills/
│   └── mc-modpack-helper/
│       └── SKILL.md    # Trae Work skill for modpack diagnostics
├── package.json        # Node.js dependencies (@modelcontextprotocol/sdk, zod)
├── tsconfig.json       # TypeScript config (CommonJS output)
├── .gitignore
├── test.js             # Integration test runner
├── test_logs/          # Test output logs (gitignored)
└── backups/            # Backup snapshots from tests (gitignored)

The MCP uses the official @modelcontextprotocol/sdk v1.x with McpServer and StdioServerTransport. All tools use server.tool() registration pattern compatible with the MCP SDK specification.

Skills

This repository also includes a Trae Work skill for modpack diagnostics. After cloning, copy the skill to your Trae Work skills directory:

Windows (PowerShell):

copy skills\mc-modpack-helper\SKILL.md "$env:USERPROFILE\.trae\skills\mc-modpack-helper\SKILL.md"

macOS / Linux:

mkdir -p ~/.trae/skills/mc-modpack-helper
cp skills/mc-modpack-helper/SKILL.md ~/.trae/skills/mc-modpack-helper/SKILL.md

See SKILL.md for the full skill documentation with 8-phase diagnostic workflow.

Testing

npm run build
MC_DIR=/path/to/your/.minecraft node test.js

Or on Windows (PowerShell):

$env:MC_DIR="C:\path\to\your\.minecraft"; node test.js

Tests create backups before running and log results to test_logs/. See individual test log files for detailed output.

Platform Compatibility

All tools accept mc_dir as an explicit path. get_java_versions auto-detects PCL on Windows; on other platforms it returns a clear message when PCL config is absent.

License

MIT