Claude MCP Approval Server

A Model Context Protocol (MCP) server that provides approval prompts via WhatsApp before executing potentially sensitive commands. Built with FastMCP and Twilio.

Features

• 🔐 Permission Prompts: Intercepts tool executions and requests approval via WhatsApp
• 📱 WhatsApp Integration: Uses Twilio to send approval requests with quick-reply buttons
• ⚡ FastMCP: Built on FastMCP for easy integration with Claude
• 🎯 Smart Formatting: Formats commands and reasons in a readable way
• ⏱️ Auto-expiry: Requests expire after 5 minutes for security
• 💾 Database Tracking: SQLite database to track approval requests

Setup Instructions

1. Install Dependencies

uv install

2. Set Up Twilio Account

1. Sign up to Twilio at https://www.twilio.com

2. Try WhatsApp messaging - Go to https://console.twilio.com/us1/develop/sms/try-it-out/whatsapp-learn and follow the setup guide to:

• Join the WhatsApp Sandbox by sending a message to the Twilio number
• Test sending/receiving messages from your device
• Note your sandbox WhatsApp number (e.g., whatsapp:+14155238886)

3. Get Twilio Credentials

1. Get your Account SID from the Twilio Console dashboard

2. Generate an Auth Token at https://console.twilio.com/us1/account/keys-credentials/api-keys

• Click "Create API Key"
• Note the SID and Secret (this is your Auth Token)

4. Configure Environment

cp .env.example .env

Edit .env with your credentials:

TWILIO_ACCOUNT_SID=your_account_sid_here
TWILIO_AUTH_TOKEN=your_auth_token_here  
TWILIO_WHATSAPP_FROM=whatsapp:+14155238886  # Your sandbox number
APPROVAL_PHONE=+1234567890  # YOUR phone number (without whatsapp: prefix)
SERVER_PORT=8000  # Optional: Server port (defaults to 8000)

Important: Replace +1234567890 with your actual phone number that you used to join the WhatsApp sandbox. This is where approval requests will be sent.

5. Create WhatsApp Template

python setup_template.py

This automatically creates the Twilio template and updates your .env file with the template SID.

6. Expose the Server

Expose your local server using ngrok or Tailscale:

Option A: ngrok

ngrok http 8000  # Replace 8000 with your SERVER_PORT if different

Option B: Tailscale

tailscale funnel --bg 8000  # Replace 8000 with your SERVER_PORT if different

Note your public URL (e.g., https://abc123.ngrok.io or https://hostname.tail12345.ts.net)

7. Configure Twilio Webhook

1. Go back to the Try WhatsApp page: https://console.twilio.com/us1/develop/sms/try-it-out/whatsapp-learn

2. Click Sandbox Settings

3. Set both webhook URLs to: https://your-public-url/twilio-webhook

• When a message comes in: https://your-public-url/twilio-webhook
• Status callback URL: https://your-public-url/twilio-webhook

8. Start the Approval Server

Important: Start the server BEFORE running Claude!

uv run  approval_server.py

The server should show:

• ✅ Twilio configured
• 🌐 Server endpoints listed
• Webhook URL ready

9. Run Claude with Permission Prompts

claude --mcp-config mcp-servers.json \
       --mcp-debug \
       --permission-prompt-tool mcp__approval-server__permissions__approve \
       --verbose \
       --debug \
       --output-format stream-json \
       -p "your prompt here"

10. Approve/Deny from Anywhere! 🎉

When Claude tries to execute a command, you'll receive a WhatsApp message with ✅ Approve and ❌ Deny buttons. Tap to respond from anywhere in the world!

Important Caveats

⚠️ Network Access: The -p (prompt) mode has no network access

⚠️ Interactive Mode: Non-interactive mode (without -p) does not use the --permission-prompt-tool

MCP Configuration

The MCP configuration is in mcp-servers.json.

Replace 8000 with your SERVER_PORT if you're using a different port.

How It Works

1. Tool Interception: When Claude tries to execute a tool, the permissions__approve function is called first

2. WhatsApp Notification: An approval request is sent to your WhatsApp with formatted command details

3. User Response: You can approve or deny using the quick-reply buttons

4. Execution: Based on your response, Claude either proceeds or stops

Message Format

Bash commands:

🔔 Approval Request

Execute command: `ls -la /etc`
*Reason:* List system configuration files

*Request ID:* abc123

⏱️ Expires in 5 minutes

Other tools:

🔔 Approval Request

*Tool:* WebFetch
  • url: https://example.com
  • prompt: Extract title

*Request ID:* abc123

⏱️ Expires in 5 minutes

Customizing the Template

To modify the WhatsApp message format or buttons:

1. Edit template_config.json

2. Run python setup_template.py to create a new template

3. The script will update your .env file with the new SID

Security & Features

• ⏱️ Auto-expiry: Requests expire after 5 minutes
• 🔒 Phone verification: Only responses from your configured phone number are accepted
• 📊 Audit trail: Database stores request history for tracking
• 🔐 E2E encryption: WhatsApp messages use end-to-end encryption
• 🌍 Global access: Approve/deny from anywhere with WhatsApp

Credits

https://github.com/mmarcen/test_permission-prompt-tool for providing a working example of using an MCP server with permission prompt tool.