System Designer MCP Server

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A Model Context Protocol (MCP) server that provides AI agents with tools to create, validate, and export UML system models and System Runtime bundles. Built with a tool-based approach that empowers LLMs to generate complete, executable System Runtime applications.

📚 Documentation

• API Reference - Detailed API documentation for all MCP tools

• System Runtime Integration Guide - Complete guide to System Runtime bundle creation

• Cloudflare Deployment Guide - Deploy to Cloudflare Workers as remote MCP server

• CLI Guide - Command-line interface usage and examples

• Integration Guide - Platform integration instructions

• Examples - Sample models and use cases

• Contributing Guide - How to contribute to the project

• Code of Conduct - Community guidelines and behavior expectations

• Security Policy - Security vulnerability reporting and policies

Related MCP server: OpenKer Modeler MCP Server

Features

Core MSON Tools

• create_mson_model: Create and validate MSON models from structured data

• validate_mson_model: Validate MSON model consistency and completeness

• generate_uml_diagram: Generate UML diagrams in PlantUML and Mermaid formats

• export_to_system_designer: Export models to System Designer application format

System Runtime Tools

• create_system_runtime_bundle: Convert MSON models to complete System Runtime bundles

• validate_system_runtime_bundle: Validate System Runtime bundles for correctness and compatibility

Key Capabilities

• ✅ Tool-Based Architecture: LLMs handle understanding, server handles validation/formatting

• ✅ Type Safety: Comprehensive Zod schema validation for all inputs and outputs

• ✅ System Runtime Integration: Full support for System Runtime bundle generation and validation

• ✅ Bidirectional Relationships: Automatic bidirectional relationship creation

• ✅ Multiple Inheritance: Support for classes implementing multiple interfaces

• ✅ Multiple UML Formats: Support for both PlantUML and Mermaid diagram generation

• ✅ System Designer Integration: Direct export to System Designer macOS application

• ✅ Comprehensive Testing: 46 tests with 302 expect() calls covering all functionality

• ✅ Critical Bug Fixes: Resolved SDMCP-001 through SDMCP-005 (property preservation, ID management, validation consistency)

• ✅ Streamable HTTP Transport: Modern MCP protocol (2025-03-26 specification)

• ✅ Stateless Operation: Each request creates new server instance

• ✅ Single Endpoint: Single /mcp endpoint handles all operations

• ✅ Workers Optimized: Stateless design perfect for Cloudflare Workers

Installation

Prerequisites

• Bun JavaScript runtime

• Node.js compatibility through Bun

Setup

# Clone the repository
git clone https://github.com/chevyphillip/system-designer-mcp.git
cd system-designer-mcp

# Install dependencies
bun install

# Build the project
bun run build

# Run tests
bun test

Quick Start

# Clone the repository
git clone https://github.com/chevyphillip/system-designer-mcp.git
cd system-designer-mcp

# Install dependencies
bun install

# Build the project
bun run build

# Run tests
bun test

Deployment Options

The System Designer MCP Server can run in two modes:

Local Mode (stdio transport)

Start the local server:

bun run dev

Remote Mode (Cloudflare Workers)

Deploy as a remote MCP server accessible over HTTP with SSE transport:

# Test locally with Wrangler
bun run dev:worker

# Deploy to Cloudflare Workers
bunx wrangler login
bun run deploy

Your MCP server will be available at:

https://system-designer-mcp.<your-subdomain>.workers.dev

Note: Replace <your-subdomain> with your actual Cloudflare Workers subdomain.

Key Features:

• ✅ SSE (Server-Sent Events) transport for remote access

• ✅ No authentication required (configurable)

• ✅ All 6 MCP tools available

• ✅ Returns JSON data directly (no file system)

• ✅ Automatic session management

• ✅ CORS support for web clients

See CLOUDFLARE_DEPLOYMENT.md for detailed deployment instructions.

Usage Examples

Example tool usage:

// Create a MSON model
const model = await mcpClient.callTool('create_mson_model', {
 name: 'Student Management System',
 type: 'class',
 description: 'A system for managing students and courses',
 entities: [
 {
 id: 'student',
 name: 'Student',
 type: 'class',
 attributes: [
 { name: 'id', type: 'string', visibility: 'private' },
 { name: 'name', type: 'string', visibility: 'public' },
 ],
 methods: [{ name: 'enroll', returnType: 'void', visibility: 'public' }],
 },
 ],
 relationships: [],
});

// Generate UML diagram
const diagram = await mcpClient.callTool('generate_uml_diagram', {
 model: model.content[1].json,
 format: 'plantuml',
});

// Export to System Designer
const exported = await mcpClient.callTool('export_to_system_designer', {
 model: model.content[1].json,
 filePath: './student_system.json',
});

// Create System Runtime bundle
const bundle = await mcpClient.callTool('create_system_runtime_bundle', {
 model: model.content[1].json,
 version: '1.0.0',
});

// Validate System Runtime bundle
const validation = await mcpClient.callTool('validate_system_runtime_bundle', {
 bundle: bundle.content[2].text, // JSON bundle from previous step
});

CLI Usage

The server includes a CLI tool for testing and model management:

# Test System Designer integration
bun run src/cli.ts test-integration

# Export a test model
bun run src/cli.ts export-model MyModel "Test model description"

# Show configuration
bun run src/cli.ts config

See the CLI Guide for detailed usage instructions.

Example MSON Model Structure

{
 "id": "student_system",
 "name": "Student Management System",
 "type": "class",
 "description": "A system for managing students and courses",
 "entities": [
 {
 "id": "student",
 "name": "Student",
 "type": "class",
 "attributes": [
 {
 "name": "id",
 "type": "string",
 "visibility": "private"
 },
 {
 "name": "name",
 "type": "string",
 "visibility": "public"
 }
 ],
 "methods": [
 {
 "name": "enroll",
 "parameters": [
 {
 "name": "course",
 "type": "Course"
 }
 ],
 "returnType": "void",
 "visibility": "public"
 }
 ]
 }
 ],
 "relationships": [
 {
 "id": "enrollment",
 "from": "student",
 "to": "course",
 "type": "association",
 "multiplicity": {
 "from": "1",
 "to": "0..*"
 },
 "name": "enrolls in"
 }
 ]
}

Tool Reference

For detailed API documentation, see the API Reference.

Available Tools

• create_mson_model - Create and validate MSON models from structured data with automatic ID generation and relationship mapping

• validate_mson_model - Validate MSON model consistency and completeness with detailed error messages and relationship validation

• generate_uml_diagram - Generate UML diagrams in PlantUML and Mermaid formats

• export_to_system_designer - Export models to System Designer application format

• create_system_runtime_bundle - Convert MSON models to complete System Runtime bundles with schemas, models, types, behaviors, and components

• validate_system_runtime_bundle - Validate System Runtime bundles for correctness and compatibility

Platform Integration

The server can be integrated with various platforms:

• Claude Desktop - Native MCP integration

• VS Code - Extension development support

• Web Applications - React/Node.js integration

• CLI Tools - Command-line interface

See the Integration Guide for detailed setup instructions.

Architecture

Modular Structure

The codebase follows SOLID principles with clear separation of concerns:

• src/types.ts - TypeScript type definitions for MSON models

• src/schemas.ts - Zod validation schemas for all data structures

• src/tools.ts - MCP tool registration using modern SDK patterns

• src/index.ts - Local MCP server with stdio transport (Node.js/Bun)

• src/worker.ts - Remote MCP server with SSE transport (Cloudflare Workers)

• src/cli.ts - Command-line interface for testing and integration

• src/integration/ - System Designer app integration

• src/transformers/ - MSON to System Runtime transformation logic

• src/validators/ - System Runtime bundle validation logic

Modern MCP SDK Patterns

The server uses the modern MCP TypeScript SDK (v1.18.2) patterns:

1. server.registerTool() - Modern tool registration API (not legacy server.tool())

2. Zod Input Schemas - Type-safe input validation with Zod schema shapes

3. Title Metadata - Each tool includes a title field for better UX

4. Type Inference - Handler methods use Zod-inferred types for parameters

Tool-Based Approach

This server uses a tool-based architecture that:

1. Empowers LLMs: The LLM handles understanding requirements and creating structured data

2. Validates Input: Server validates structured input using comprehensive Zod schemas

3. Processes Efficiently: Simple, fast processing without complex parsing logic

4. Exports Flexibly: Multiple output formats for different use cases

Benefits Over Parser-Based Approaches

• Simplicity: No complex NLP parsing to maintain

• Flexibility: Works with any domain the LLM understands

• Reliability: Fewer moving parts, less error-prone

• Performance: Faster validation and processing

• Extensibility: Easy to add new tools and features

Development

Running Tests

# Run all tests
bun test

# Run tests in watch mode
bun test --watch

Building

# Build for production
bun run build

# Start production server
bun start

Code Structure

src/
├── types.ts # TypeScript type definitions for MSON models
├── schemas.ts # Zod validation schemas for all data structures
├── tools.ts # MCP tool registration using modern SDK patterns
├── index.ts # Local MCP server (stdio transport)
├── worker.ts # Remote MCP server (SSE transport for Workers)
├── cli.ts # Command-line interface
├── integration/
│ └── system-designer.ts # System Designer app integration
├── transformers/
│ └── system-runtime.ts # MSON to System Runtime transformation
└── validators/
 └── system-runtime.ts # System Runtime bundle validation

test/
└── tool-based.test.ts # Comprehensive test suite

docs/
├── API-REFERENCE.md # Detailed API documentation
├── CLI-GUIDE.md # CLI usage guide
├── INTEGRATION-GUIDE.md # Platform integration guide
└── SYSTEM-RUNTIME-INTEGRATION-GUIDE.md # System Runtime guide

examples/
├── banking-system.json # Sample banking system model
├── banking-system-plantuml.puml # PlantUML output example
├── banking-system-mermaid.md # Mermaid output example
└── README.md # Example documentation

CLOUDFLARE_DEPLOYMENT.md # Cloudflare Workers deployment guide
test-worker.sh # Automated testing script for Workers
wrangler.toml # Cloudflare Workers configuration

Integration with System Designer

The server exports models in a format compatible with the System Designer macOS application:

1. File Export: Models are saved as JSON files

2. Automatic Integration: Files can be imported directly into System Designer

3. Format Compatibility: Uses MSON (Metamodel JavaScript Object Notation) format

Recent Changes & Improvements

Latest Updates (v1.0.0)

• 🎯 Critical Bug Fixes (SDMCP-001-005): Resolved property preservation, ID mapping, validation consistency, and bundle compatibility issues

• 🔧 Enhanced Error Messages: Added detailed, actionable error messages with specific fix suggestions and examples

• 🛡️ Relationship Validation: Proactive validation prevents orphaned references with clear guidance

• 🔄 Flexible Input Handling: Support for both 'properties' and 'attributes' in entity definitions

• 📋 Comprehensive Bug Reports: Detailed documentation of all issues and resolutions in docs/BUG_REPORTS.md

• 🆕 System Runtime Tools: Added complete System Runtime bundle creation and validation functionality

Previous Features

• 🏗️ Modular Architecture: Complete refactoring for SOLID principles compliance

• 🧪 Enhanced Testing: 46 tests with 302 assertions covering all functionality including edge cases

• 🚀 Cloudflare Workers Support: Remote MCP server deployment with modern JSON-RPC transport

• 🔄 Modern MCP SDK: Updated to latest MCP TypeScript SDK (v1.18.2) patterns

• 📊 Documentation: Complete API reference, integration guides, and deployment documentation

Contributing

We welcome contributions! Please see our Contributing Guide for details on:

• Setting up the development environment

• Running tests and code quality checks

• Code style guidelines

• Submitting pull requests

• Reporting issues

License

MIT License - see LICENSE file for details.

Acknowledgments

• Model Context Protocol (MCP) for the tool integration framework

• System Designer for the target macOS application

• Zod for type-safe validation

• Bun for the fast JavaScript runtime

Maintenance

Resources

• GitHub Repository
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