How do I install X402 Sms?

Copy the stdio config for Cursor, Claude Desktop, Claude Code, or VS Code on this page. It uses the publisher's install, not a PlugMCP proxy.

Does X402 Sms need an API key?

The publisher lists these environment variables: BUYER_PRIVATE_KEY.

What transport does X402 Sms use?

X402 Sms runs locally over stdio.

When was X402 Sms last checked?

Last checked 2026-11-09. Pay-per-call MCP server. $0.03 USDC sends one transactional SMS to a US phone number via x402.

X402 Sms MCP server

Power your agent

Add this server

The publisher's own command. Not a PlugMCP endpoint.

Add to Cursor Add to VS Code Run on PlugMCP

Host a copy with our keys and logs.

Local command

npx -y [email protected]

Credentials from the publisher

BUYER_PRIVATE_KEY — Ethereum private key for the buyer wallet that pays the per-call USDC fee.

Claude Code has no install link for a local command. Copy the command below and run it in a terminal.

shClaude Code

1BUYER_PRIVATE_KEY=<secret> claude mcp add io.github.ultrastarz-x402-sms -- npx -y x402-sms-mcp@0.1.0

Run in a terminal.

jsonClaude Desktop

1{2  "mcpServers": {3    "io.github.ultrastarz-x402-sms": {4      "command": "npx",5      "args": [6        "-y",7        "[email protected]"8      ],9      "env": {10        "BUYER_PRIVATE_KEY": "<secret>"11      }12    }13  }14}

claude_desktop_config.json

Local · npmPublisher installStep-by-step: add this in Claude

Remote URL or a command on your machine? How the two installs differ

Run on PlugMCP

Host a copy with our keys and logs.

A new server you create. It is not this listing's official endpoint. Use the publisher install when you want their URL and their credentials.

Launch

Server facts

Local

Transport: stdio
Version: 0.1.0
API key

Tools

No tool list yet. Remote servers get one after the first health check.

FAQ

Questions

x402-sms-mcp

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

Each send_sms tool call:

Sends a transactional SMS via the seller's toll-free number (Twilio verification in progress)
Auto-appends Reply STOP to opt out if the body doesn't include opt-out language
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 delivery_pending_tfv_approval 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/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

Env var	Required	Default
`BUYER_PRIVATE_KEY`	yes	—
`SMS_URL`	no	`https://x402-sms-server-production.up.railway.app/send`

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.

Cause	What you'll see in chat	Was payment taken?
Seller's toll-free number still in TFV review (`HTTP 503`)	"SMS not sent — service is in pre-launch wait" + the seller's submitted date and retry guidance	no
Buyer wallet exceeded per-minute/hour/day rate limit (`HTTP 429`)	"SMS not sent — this buyer wallet hit the per-X rate limit" + `retry_after_seconds`	no
Twilio-side rejection (e.g. invalid number `21211`, opted-out `21610`)	Friendly hint mapped from the Twilio error code + the full response body	yes (the send tried)

For the full mapping of Twilio error codes the MCP recognizes, see TWILIO_HINTS in src/index.ts.

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 toll-free number dispatches the SMS. Your private key never leaves your machine. The seller never sees it.

Roadmap

Now (2026-05-22): Base Sepolia testnet, TFV pending. Payment flow verified end-to-end; deliveries gated on Twilio approval.
Once TFV clears: Real US SMS delivery, testnet pricing held while we collect early traffic.
A few weeks out: A2P 10DLC Brand approval → higher per-day throughput tier.
Mainnet flip: Production launch, USDC settles on Base mainnet; Solana facilitator on roadmap after.

License

MIT

Add this server

Host a copy with our keys and logs.

Server facts

Tools

Questions

How do I install X402 Sms?

Does X402 Sms need an API key?

What transport does X402 Sms use?

When was X402 Sms last checked?

Documentation

x402-sms-mcp

Install in Claude Desktop / Cursor / Windsurf

What you need

Try it

Compliance — please read

Configuration

Errors you might see

How it works

Roadmap

License