Mermaid MCP Server

A lightweight Model Context Protocol (MCP) server that provides real-time Mermaid diagram syntax validation with minimal memory footprint.

Features

• ✅ Real-time Syntax Validation: Instant validation while you edit diagrams
• 🚀 Ultra Lightweight: Minimal memory usage, optimized for performance
• 🎯 100% Compatibility: Supports all Mermaid diagram types
• 📊 Detailed Error Reporting: Line numbers, error classification, and suggestions
• 🔧 Batch Validation: Validate multiple diagrams at once
• 📈 Performance Monitoring: Track validation times and memory usage

Supported Diagram Types

• Flowcharts (graph, flowchart)
• Sequence Diagrams (sequenceDiagram)
• Class Diagrams (classDiagram)
• State Diagrams (stateDiagram)
• Entity Relationship Diagrams (erDiagram)
• Gantt Charts (gantt)
• User Journey (journey)
• Pie Charts (pie)
• Git Graphs (gitgraph)
• Mind Maps (mindmap)
• Timelines (timeline)
• C4 Architecture (c4)
• Sankey Diagrams (sankey)
• Block Diagrams (block)
• Architecture Diagrams (architecture)

Installation

1. Clone this repository:

git clone <repository-url>
cd mermaid-mcp-server

2. Install dependencies:

npm install

3. Add to your MCP client configuration:

Claude Desktop Configuration

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "mermaid": {
      "command": "node",
      "args": ["/path/to/mermaid-mcp-server/server.js"],
      "env": {}
    }
  }
}

Usage Examples

Basic Syntax Validation

// Validate a simple flowchart
const result = await validate_mermaid({
  diagramCode: `graph TD
    A[Start] --> B{Decision}
    B -->|Yes| C[Process]
    B -->|No| D[End]
    C --> D`
});

Real-time Validation Hook

// Real-time validation during editing
const realtimeResult = await mermaid_realtime_validate({
  diagramCode: "sequenceDiagram\n    A->>B: Hello",
  changeType: "add",
  lineNumber: 2
});

Batch Validation

// Validate multiple diagrams at once
const batchResult = await validate_mermaid_batch({
  diagrams: [
    "graph TD\n    A --> B",
    "sequenceDiagram\n    A->>B: Test",
    "invalid diagram code"
  ]
});

API Reference

Tools

validate_mermaid

Validates a single Mermaid diagram.

Parameters:

• diagramCode (string, required): The Mermaid diagram code to validate

Returns:

{
  "isValid": true,
  "error": null,
  "type": null,
  "line": null,
  "suggestion": null,
  "processingTime": 12,
  "diagramType": "graph",
  "elementCount": 4
}

mermaid_realtime_validate

Real-time validation for live editing scenarios.

Parameters:

• diagramCode (string, required): Current diagram code
• changeType (string, required): Type of change (add, remove, modify, full)
• lineNumber (number, optional): Line where change occurred

Returns: Enhanced validation result with change metadata.

validate_mermaid_batch

Validates multiple diagrams in a single call.

Parameters:

• diagrams (array, required): Array of diagram codes

Returns:

{
  "summary": {
    "total": 3,
    "valid": 2,
    "invalid": 1,
    "averageProcessingTime": 15.3
  },
  "results": [...]
}

get_mermaid_info

Gets server information and supported diagram types.

Returns:

{
  "server": {
    "name": "mermaid-mcp-server",
    "version": "1.0.0",
    "uptime": 3600
  },
  "supportedTypes": [...],
  "stats": {...},
  "features": [...]
}

Error Types

The server classifies errors into these categories:

• syntax: General syntax errors
• no_type: Missing diagram type declaration
• unknown_command: Unsupported commands
• parse: Parsing errors
• identifier: Invalid identifiers
• relation: Connection/arrow issues
• general: Other errors

Performance Optimization

Memory Management

• Lazy initialization of Mermaid engine
• Minimal dependencies
• Efficient garbage collection
• No DOM rendering (validation only)

Processing Speed

• Direct Mermaid parsing without rendering
• Optimized error extraction
• Batch processing capabilities
• Performance metrics tracking

Usage Tips

1. Use mermaid_realtime_validate for live editing
2. Use validate_mermaid_batch for multiple diagrams
3. Check processingTime to monitor performance
4. Monitor memory usage with get_mermaid_info

Development

Running in Development Mode

npm run dev

Testing

# Test with various diagram types
node test.js

Environment Variables

• NODE_ENV: Set to development for debug logging
• GC_INTERVAL: Garbage collection interval (default: 60000ms)

Configuration

The server can be configured via environment variables:

# Enable debug logging
DEBUG=mermaid-mcp-server

# Set memory limit (MB)
MEMORY_LIMIT=128

# Enable performance monitoring
PERFORMANCE_MONITORING=true

Troubleshooting

Common Issues

1. Server won't start

   • Check Node.js version (>=18.0.0 required)
   • Verify all dependencies are installed
   • Check for port conflicts if applicable

2. Memory usage high

   • Restart server periodically
   • Use batch validation instead of many single calls
   • Monitor memory usage via get_mermaid_info

3. Validation errors

   • Ensure proper diagram syntax
   • Check supported diagram types
   • Use real-time validation for immediate feedback

Debug Mode

Enable debug logging:

DEBUG=mermaid-mcp-server:* npm start

License

MIT License

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests if applicable
5. Submit a pull request

Support

For issues and questions:

• Create an issue on GitHub
• Check the troubleshooting section
• Review the API documentation