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 (2026-05-22): Public beta on Base Sepolia (testnet). The seller's toll-free number is undergoing Twilio TFV approval (submitted 2026-05-14, still in queue). During this window /send calls short-circuit to a 503 deliverypendingtfvapproval response before** the buyer wallet signs anything, so no USDC is moved. The day Twilio approves the number, delivery flips on; pricing flips to Base mainnet shortly after.

Install in Claude Desktop / Cursor / Windsurf

Add this to your MCP config (~/Library/Application Support/Claude/claudedesktopconfig.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 )
• USDC for payments (free from , 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 sendsms with optin_attestation: true. You'll get back a Twilio SID + the on-chain settlement hash. The transfer is visible at .

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 sendsms. The optin_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.

Errors you might see

The MCP surfaces three distinct error shapes so the model can explain what happened to the user and decide whether to retry.

Shortened. The full README is on GitHub.