MCreator MCP Integration Plugin

A lightweight Model Context Protocol (MCP) server implementation for MCreator that enables LLM applications to interact with MCreator workspaces, build projects, manage mod elements, and access workspace resources.

Features

🛠️ Direct Integration

• Native MCP server implementation without external dependencies
• Direct MCreator API integration for optimal performance
• JSON-RPC 2.0 protocol compliance according to MCP specification
• No separate JAR processes or IPC overhead

🔧 Core Tools

• Workspace Management: Build, regenerate code, get info, settings
• Element Operations: List, create, edit, delete mod elements
• Testing: Run Minecraft client/server with mods
• Resources: Access workspace overview, elements, project structure

🌐 Multiple Transport Support

• HTTP: http://localhost:<port>/mcp (standard MCP protocol)
• SSE: http://localhost:<port>/mcp/sse (legacy compatibility)
• Stdio: Traditional MCP client support
• Health: http://localhost:<port>/health (monitoring)

📊 Rich Resources

• Complete workspace overview with metadata and statistics
• Project structure and file organization
• Live workspace statistics and element information
• Configuration and build information

Quick Start

Prerequisites

• Java 21+
• MCreator 2025.2+
• Git (for development)

Installation

1. Download/Build the Plugin:

   git clone <repository-url>
   cd MCreatorMCP1
   ./gradlew jar
   

2. Install Plugin:

   • Copy build/libs/MCreatorMCP.zip to your MCreator plugins folder
   • Or use ./gradlew runMCreatorWithPlugin for development

3. Enable Java Plugins in MCreator preferences

4. Start MCreator - the MCP server will start automatically

Connecting LLM Clients

The MCP server exposes endpoints at (default port 5175 unless dynamically selected):

• HTTP: http://localhost:<port>/mcp (standard MCP protocol)
• SSE: http://localhost:<port>/mcp/sse (legacy compatibility)
• Stdio: Connect directly via stdin/stdout for traditional MCP clients
• Health Check: http://localhost:<port>/health

Configure your MCP-compatible client to connect to one of these endpoints.

Architecture

Simplified Direct Integration

┌─────────────────┐     Direct      ┌─────────────────┐
│   MCreator      │◄───────────────►│   LLM Client    │
│   + MCP Plugin  │    MCP Protocol │   (Editor/Agent)│
└─────────────────┘                 └─────────────────┘

• MCreator Plugin: Contains integrated MCP server with direct API access
• No External Processes: Everything runs within the plugin JVM
• Direct Integration: No IPC overhead, immediate MCreator API access
• Clean Architecture: Lightweight, fast, and maintainable

Note: Ports are dynamically selected to avoid conflicts. Check the plugin status dialog or logs for the actual port.

Project Structure

MCreatorMCP/
├── src/main/java/net/mcreator/MCreatorMCP/
│   ├── MCreatorMCP.java              # Main plugin entry point
│   ├── MCPToolsService.java          # MCreator tool implementations
│   └── mcp/                          # MCP server implementation
│       ├── McpServer.java            # Core MCP server
│       ├── JsonRpcMessage.java       # JSON-RPC message handling
│       ├── McpTypes.java             # MCP protocol data types
│       ├── McpHttpTransport.java     # HTTP/SSE transport
│       └── McpStdioTransport.java    # Stdio transport
├── build.gradle                     # Plugin build configuration
└── settings.gradle                  # Project setup

Available Tools

Workspace Management

• buildWorkspace() - Build the current workspace
• getWorkspaceInfo() - Get detailed workspace information
• regenerateCode() - Regenerate code without building

Element Operations

• listModElements(elementType?) - List mod elements with optional filtering
• openElement(elementName) - Open element in MCreator UI
• createElement(elementType, elementName) - Create new mod element
• deleteElement(elementName) - Delete mod element

Testing & Execution

• runClient() - Start Minecraft client
• runServer() - Start Minecraft server

Resource Management

• listTextures() - List texture files
• listSounds() - List sound files
• listStructures() - List structure files

Variables & Localization

• listVariables() - List workspace variables
• createVariable(name, type, scope) - Create new variable
• getLocalizations(language?) - Get localization entries

Resources

Available Resources

• workspace://overview - Complete workspace overview with metadata
• workspace://elements - All mod elements with properties and details
• workspace://structure - Project directory structure and organization

Configuration

The MCP server is automatically configured by the plugin with sensible defaults:

• HTTP Port: Auto-selected starting from 5175
• Transport Methods: HTTP, SSE, and Stdio enabled by default
• Workspace Integration: Automatic detection when MCreator workspace loads
• Tool Registration: All MCreator tools automatically registered

No additional configuration needed - just install and run!

Development

Building

# Build the plugin
./gradlew jar

# Run MCreator with plugin
./gradlew runMCreatorWithPlugin

# Clean build
./gradlew clean build

Debugging

• Plugin logs: MCreator console output
• MCP Protocol: Enable DEBUG logging in MCreator console
• Network traffic: Monitor HTTP endpoints with browser dev tools

Testing Tools

# Test MCP endpoints
curl http://localhost:<port>/health
curl -X POST http://localhost:<port>/mcp \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test-client","version":"1.0"}}}'

Troubleshooting

Common Issues

MCP Server won't start:

• Check Java 21+ is available
• Verify the HTTP port is free (default 5175). The plugin will auto-select a free port.
• Check MCreator console for errors

Tools not working:

• Ensure MCreator workspace is loaded
• Check plugin status via "MCP Server Status" menu
• Restart MCP server if needed

Client connection issues:

• Try different transport methods (HTTP vs SSE vs Stdio)
• Check CORS settings for web clients
• Verify MCP client protocol version compatibility

Monitoring

• Health checks: http://localhost:<port>/health
• Plugin status: "MCP Server Status" menu in MCreator
• Console logs: Enable DEBUG logging in MCreator

Contributing

1. Fork the repository
2. Create a feature branch
3. Implement changes with tests
4. Update documentation
5. Submit a pull request

License

This project is licensed under the GNU General Public License v3.0 - see the LICENSE file for details.

Links

• MCreator - Minecraft mod creation platform
• Model Context Protocol - Protocol specification
• MCreator Plugin Development - Plugin development guide