The Penpot MCP Server

This system enables LLMs to interact with Penpot design projects through a Model Context Protocol (MCP) server and plugin architecture.

Architecture

The system consists of three main components:

1. Common Types (common/):

   • Shared TypeScript definitions for request/response protocol
   • Ensures type safety across server and plugin components
   • Defines PluginTaskResult, request/response interfaces, and task parameters

2. MCP Server (mcp-server/):

   • Provides MCP tools to LLMs for Penpot interaction
   • Runs WebSocket server accepting connections from Penpot plugins
   • Implements request/response correlation with unique task IDs
   • Handles task timeouts and proper error reporting

3. Penpot Plugin (penpot-plugin/):

   • Connects to MCP server via WebSocket
   • Executes tasks in Penpot using the Plugin API
   • Sends structured responses back to server with success/failure status

Protocol Flow

LLM → MCP Server → WebSocket → Penpot Plugin → Penpot API
     ↓                      ↓               ↓
   Tool Call          Task Request    Execute Action
     ↑                      ↑               ↑
LLM ← MCP Server ← WebSocket ← Penpot Plugin ← Result

Request Format

{
  id: string,           // Unique UUID for correlation
  task: string,         // Task type (e.g., "printText")
  params: object        // Task-specific parameters
}

Response Format

{
  id: string,           // Matching request ID
  result: {
    success: boolean,   // Task completion status
    error?: string,     // Error message if failed
    data?: any         // Optional result data
  }
}

Testing the Connection

Step 1: Start the MCP Server

cd mcp-server
npm run build
npm start

Step 2: Build and Run the Plugin

cd penpot-plugin
npm run build
npm run dev

Step 3: Load Plugin in Penpot

1. Open Penpot in your browser
2. Navigate to a design file
3. Go to Plugins menu
4. Load the plugin using the development URL (typically http://localhost:4400/manifest.json)
5. Open the plugin UI

Step 4: Test the Connection

1. In the plugin UI, click "Connect to MCP server"
2. The connection status should change from "Not connected" to "Connected to MCP server"
3. Check the browser's developer console for WebSocket connection logs
4. Check the MCP server terminal for WebSocket connection messages

Step 5: Use an MCP Client to Interact with the Penpot Project

See MCP Server README