Excalidraw MCP Canvas: Live Visual Diagramming with AI Integration

A comprehensive system that combines Excalidraw's powerful drawing capabilities with Model Context Protocol (MCP) integration, enabling AI agents to create and manipulate diagrams in real-time on a live canvas.

🚀 What This System Does

• 🎨 Live Canvas: Real-time Excalidraw canvas accessible via web browser
• 🤖 AI Integration: MCP server allows AI agents (like Claude) to create visual diagrams
• ⚡ Real-time Sync: Elements created via MCP API appear instantly on the canvas
• 🔄 WebSocket Updates: Live synchronization across multiple connected clients
• 🏗️ Production Ready: Clean, minimal UI suitable for end users

🏛️ Architecture Overview

┌─────────────────┐    ┌──────────────────┐    ┌─────────────────┐
│   AI Agent      │───▶│   MCP Server     │───▶│  Canvas Server  │
│   (Claude)      │    │  (src/index.js) │    │ (src/server.js) │
└─────────────────┘    └──────────────────┘    └─────────────────┘
                                                         │
                                                         ▼
                                               ┌─────────────────┐
                                               │  Frontend       │
                                               │  (React + WS)   │
                                               └─────────────────┘

🌟 Key Features

Real-time Canvas Integration

• Elements created via MCP appear instantly on the live canvas
• WebSocket-based real-time synchronization
• Multi-client support with live updates

Production-Ready Interface

• Clean, minimal UI with connection status
• Simple "Clear Canvas" functionality
• No development clutter or debug information

Comprehensive MCP API

• Element Creation: rectangles, ellipses, diamonds, arrows, text, lines
• Element Management: update, delete, query with filters
• Batch Operations: create multiple elements in one call
• Advanced Features: grouping, alignment, distribution, locking

Robust Architecture

• Express.js backend with REST API + WebSocket
• React frontend with official Excalidraw package
• Dual-path element loading for reliability
• Auto-reconnection and error handling

📦 Installation & Setup

Prerequisites

• Node.js 16+
• npm or yarn

1. Clone and Install

git clone <repository-url>
cd mcp_excalidraw
npm install

2. Build the Frontend

npm run build

3. Start the System

Option A: Production Mode

# Start canvas server (serves frontend + API)
npm run canvas

Option B: Development Mode

# Start both canvas server and Vite dev server
npm run dev

4. Access the Canvas

Open your browser and navigate to:

http://localhost:3000

🔧 Available Scripts

Script	Description
npm start	Start MCP server (src/index.js)
npm run canvas	Start canvas server (src/server.js)
npm run build	Build frontend for production
npm run dev	Start canvas + Vite dev server
npm run production	Build + start in production mode

🎯 Usage Guide

For End Users

1. Open the canvas at http://localhost:3000
2. Check connection status (should show "Connected")
3. AI agents can now create diagrams that appear in real-time
4. Use "Clear Canvas" to remove all elements

For AI Agents (via MCP)

The MCP server provides these tools for creating visual diagrams:

Basic Element Creation

// Create a rectangle
{
  "type": "rectangle",
  "x": 100,
  "y": 100, 
  "width": 200,
  "height": 100,
  "backgroundColor": "#e3f2fd",
  "strokeColor": "#1976d2",
  "strokeWidth": 2
}

Create Text Elements

{
  "type": "text",
  "x": 150,
  "y": 125,
  "text": "Process Step",
  "fontSize": 16,
  "strokeColor": "#333333"
}

Create Arrows & Lines

{
  "type": "arrow",
  "x": 300,
  "y": 130,
  "width": 100,
  "height": 0,
  "strokeColor": "#666666",
  "strokeWidth": 2
}

Batch Creation for Complex Diagrams

{
  "elements": [
    {
      "type": "rectangle",
      "x": 100,
      "y": 100,
      "width": 120,
      "height": 60,
      "backgroundColor": "#fff3e0",
      "strokeColor": "#ff9800"
    },
    {
      "type": "text", 
      "x": 130,
      "y": 125,
      "text": "Start",
      "fontSize": 16
    }
  ]
}

🔌 Integration with Claude Desktop

Add this configuration to your claude_desktop_config.json:

{
  "mcpServers": {
    "excalidraw_canvas": {
      "command": "node",
      "args": ["/path/to/mcp_excalidraw/src/index.js"],
    }
  }
}

Integration with Cursor

Add this configuration to your claude_desktop_config.json:

{
    "mcpServers": {
      "mcp_excalidraw": {
        "command": "node",
        "args": ["/path/to/mcp_excalidraw/src/index.js"]
    }
  }
}

Important: Replace /path/to/mcp_excalidraw with the actual absolute path to your installation.

🛠️ Environment Variables

Variable	Default	Description
EXPRESS_SERVER_URL	http://localhost:3000	Canvas server URL for MCP sync
ENABLE_CANVAS_SYNC	true	Enable/disable canvas synchronization
DEBUG	false	Enable debug logging
PORT	3000	Canvas server port
HOST	localhost	Canvas server host

📊 API Endpoints

The canvas server provides these REST endpoints:

Method	Endpoint	Description
GET	/api/elements	Get all elements
POST	/api/elements	Create new element
PUT	/api/elements/:id	Update element
DELETE	/api/elements/:id	Delete element
POST	/api/elements/batch	Create multiple elements
GET	/health	Server health check

🎨 MCP Tools Available

Element Management

• create_element - Create any type of Excalidraw element
• update_element - Modify existing elements
• delete_element - Remove elements
• query_elements - Search elements with filters

Batch Operations

• batch_create_elements - Create complex diagrams in one call

Element Organization

• group_elements - Group multiple elements
• ungroup_elements - Ungroup element groups
• align_elements - Align elements (left, center, right, top, middle, bottom)
• distribute_elements - Distribute elements evenly
• lock_elements / unlock_elements - Lock/unlock elements

Resource Access

• get_resource - Access scene, library, theme, or elements data

🏗️ Development Architecture

Frontend (frontend/src/)

• React + Vite: Modern build system
• Official Excalidraw: @excalidraw/excalidraw package
• WebSocket Client: Real-time element sync
• Clean UI: Production-ready interface

Canvas Server (src/server.js)

• Express.js: REST API + static file serving
• WebSocket: Real-time client communication
• Element Storage: In-memory with persistence options
• CORS: Cross-origin support

MCP Server (src/index.js)

• MCP Protocol: Standard Model Context Protocol
• Canvas Sync: HTTP requests to canvas server
• Element Management: Full CRUD operations
• Batch Support: Complex diagram creation

🐛 Troubleshooting

Canvas Not Loading

• Ensure npm run build completed successfully
• Check that dist/index.html exists
• Verify canvas server is running on port 3000

Elements Not Syncing

• Confirm MCP server is running (npm start)
• Check ENABLE_CANVAS_SYNC=true in environment
• Verify canvas server is accessible at EXPRESS_SERVER_URL

WebSocket Connection Issues

• Check browser console for WebSocket errors
• Ensure no firewall blocking WebSocket connections
• Try refreshing the browser page

Build Errors

• Delete node_modules and run npm install
• Check Node.js version (requires 16+)
• Ensure all dependencies are installed

📋 Project Structure

mcp_excalidraw/
├── frontend/
│   ├── src/
│   │   ├── App.jsx          # Main React component
│   │   └── main.jsx         # React entry point
│   └── index.html           # HTML template
├── src/
│   ├── index.js            # MCP server
│   ├── server.js           # Canvas server (Express + WebSocket)
│   ├── types.js            # Shared types and utilities
│   └── utils/
│       └── logger.js       # Logging utility
├── dist/                   # Built frontend (generated)
├── vite.config.js         # Vite build configuration
├── package.json           # Dependencies and scripts
└── README.md              # This file

🤝 Contributing

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

📝 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙏 Acknowledgments

• Excalidraw Team - For the amazing drawing library
• MCP Community - For the Model Context Protocol specification