gh-claudeforge-marketplace-plugins-commands-desktop-integrator/commands/claude-desktop-extension.md

description, version

description	version
Build Claude Desktop Extensions (DXT) with proper MCP server setup and manifest configuration	1.0.0

Claude Desktop Extension Builder

Build Claude Desktop Extensions using the Model Context Protocol to extend Claude Desktop with custom tools and capabilities.

What It Does

• Creates MCP-compatible server implementations
• Generates valid extension manifest files
• Sets up proper tool definitions and schemas
• Configures stdio transport for local execution
• Enables custom functionality in Claude Desktop

How to Use

Run this command when you want to create a new Desktop Extension:

/claude-desktop-extension

The command will guide you through creating a complete extension with server code and manifest.

Example Structure

A basic DXT includes two main files:

manifest.json

{
  "name": "my-extension",
  "version": "1.0.0",
  "description": "Custom tools for Claude",
  "main": "server.js",
  "mcp": {
    "transport": "stdio"
  }
}

server.js

import { Server } from '@modelcontextprotocol/sdk/server/index.js';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';

const server = new Server({
  name: 'my-extension',
  version: '1.0.0'
}, {
  capabilities: {
    tools: {}
  }
});

server.setRequestHandler('tools/list', async () => ({
  tools: [{
    name: 'my_tool',
    description: 'Does something useful',
    inputSchema: {
      type: 'object',
      properties: {
        input: { type: 'string' }
      }
    }
  }]
}));

server.setRequestHandler('tools/call', async (request) => {
  const { name, arguments: args } = request.params;

  if (name === 'my_tool') {
    return {
      content: [{ type: 'text', text: `Processed: ${args.input}` }]
    };
  }

  throw new Error(`Unknown tool: ${name}`);
});

const transport = new StdioServerTransport();
await server.connect(transport);

Use Cases

• File System Tools: Add custom file operations beyond built-in capabilities
• API Integrations: Connect Claude to external services and APIs
• Data Processing: Create specialized data transformation tools
• System Utilities: Access system information or execute commands
• Database Access: Query and modify database contents

Best Practices

• Error Handling: Wrap tool logic in try-catch blocks and return meaningful error messages
• Input Validation: Use JSON Schema to validate tool inputs before processing
• Async Operations: Use async/await for I/O operations and external API calls
• Logging: Add console.error() for debugging (output goes to Claude Desktop logs)
• Tool Naming: Use snake_case for tool names and be descriptive
• Schema Design: Define clear input schemas with required fields and types
• Response Format: Always return structured content arrays
• Testing: Test with sample inputs before deploying to Claude Desktop

Installation

After building your extension:

1. Save files in a dedicated directory
2. Run npm install @modelcontextprotocol/sdk
3. Add to Claude Desktop config:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json Windows: %APPDATA%/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "my-extension": {
      "command": "node",
      "args": ["/path/to/your/server.js"]
    }
  }
}

4. Restart Claude Desktop

Common Patterns

Reading environment variables:

const apiKey = process.env.API_KEY;
if (!apiKey) {
  throw new Error('API_KEY not configured');
}

Making HTTP requests:

const response = await fetch('https://api.example.com/data');
const data = await response.json();
return { content: [{ type: 'text', text: JSON.stringify(data) }] };

File operations:

import fs from 'fs/promises';
const content = await fs.readFile(args.path, 'utf-8');
return { content: [{ type: 'text', text: content }] };

Troubleshooting

• Extension not appearing: Check Claude Desktop logs for connection errors
• Tool failures: Ensure proper error handling and valid return formats
• Transport issues: Verify stdio transport is configured correctly
• Schema validation: Test input schemas match your tool expectations

Resources

• DXT Documentation: https://github.com/anthropics/dxt
• MCP SDK: https://github.com/modelcontextprotocol
• Examples: https://github.com/anthropics/dxt/tree/main/examples