X402 Sms MCP Server

x402-sms-mcp

A paid MCP server that lets AI agents send SMS messages to US phone numbers.

Each send_sms tool call:

1. Sends a transactional SMS via a verified toll-free number
2. Auto-appends Reply STOP to opt out if the body doesn't include opt-out language
3. Costs $0.03 USDC per message, paid automatically from the configured wallet via x402

No API keys. No Twilio account. The agent pays the toll, the message goes out.

Status: Public beta on Base Sepolia (testnet). The seller's toll-free number is undergoing Twilio TFV approval (typically 3-5 business days from May 2026). During this window the payment flow works end-to-end on chain but Twilio will reject undelivered messages with code 30032. Once approved, messages will deliver and pricing flips to Base mainnet.

Install in Claude Desktop / Cursor / Windsurf

Add this to your MCP config (~/Library/Application Support/Claude/claude_desktop_config.json on macOS):

{
  "mcpServers": {
    "x402-sms": {
      "command": "npx",
      "args": ["-y", "x402-sms-mcp"],
      "env": {
        "BUYER_PRIVATE_KEY": "0xYOUR_PRIVATE_KEY"
      }
    }
  }
}

Restart your MCP client. A send_sms tool will appear.

What you need

A wallet on Base Sepolia (testnet) funded with:

• A small amount of ETH for gas (free from https://www.coinbase.com/faucets/base-ethereum-sepolia-faucet)
• USDC for payments (free from https://faucet.circle.com, select Base Sepolia)

Generate a throwaway key:

node -e "const {generatePrivateKey,privateKeyToAccount}=require('viem/accounts');const k=generatePrivateKey();console.log('PRIVATE_KEY=',k);console.log('ADDRESS=',privateKeyToAccount(k).address)"

Use the printed address to claim from faucets, then put the printed key into your MCP config.

Try it

In Claude Desktop, ask:

Text my cell at +15551234567 when this long-running task finishes. The recipient (me) consents to receive this message.

Claude will call send_sms with opt_in_attestation: true. You'll get back a Twilio SID + the on-chain settlement hash. The transfer is visible at https://sepolia.basescan.org.

Compliance — please read

This MCP wraps a regulated SMS gateway. The operator (you) is responsible for ensuring every recipient has consented to receive messages before invoking send_sms. The opt_in_attestation: true argument is your legal attestation under TCPA and CTIA short-code/long-code rules.

Do NOT use this MCP to:

• Send marketing or promotional content
• Text strangers, scraped lists, or anyone who hasn't opted in
• Send to non-US numbers (the seller currently rejects non-+1 E.164)
• Send anything related to S.H.A.F.T.-C (Sex, Hate, Alcohol, Firearms, Tobacco, Cannabis)

The seller-side automatically:

• Appends Reply STOP to opt out to every message
• Honors carrier-level STOP/HELP keyword handling
• Logs each send for audit purposes

If you have any doubt about consent, do not call this tool.

Configuration

To point the MCP server at your own seller deployment, override SMS_URL.

How it works

Claude Desktop ──tool call──> MCP server (this package, on your machine)
                              │
                              │ x402 payment (USDC, Base Sepolia)
                              │ + to/message/opt_in_attestation
                              ▼
                              Public seller (Hono + Twilio on Railway)
                              │
                              │ Twilio dispatch
                              ▼
                              SMS lands on recipient's phone
                              │
                              │ Twilio SID + status
                              ▼
                              MCP server ──tool result──> Claude Desktop

The MCP server doesn't talk to Twilio directly. It signs an x402 payment with the buyer's wallet, sends the payment + message details to the seller endpoint, and the seller's verified toll-free number dispatches the SMS. Your private key never leaves your machine. The seller never sees it.

Roadmap

• Now: Testnet (Base Sepolia), TFV pending. Pay flow works, delivery blocked.
• Days from now (TFV approval): Real US SMS delivery on testnet pricing.
• A few weeks (A2P 10DLC Brand approval): Higher throughput tier.
• Mainnet flip: Production launch, USDC payments settle on Base mainnet.

License

MIT