X402 Sms

io.github.UltraStarzPublished by GitHub account UltraStarzv0.1.0Updated Oct 24, 2026

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

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Overview

AI-generated overview

Lets an assistant send transactional SMS to US phone numbers, paying a per-message USDC fee from a configured wallet.

What you can do
Exposes a send_sms tool that dispatches a transactional SMS to a US (+1 E.164) number through a third-party seller's toll-free number. Each call costs $0.03 USDC, signed automatically from the configured buyer wallet via x402, and the tool returns a Twilio SID plus an on-chain settlement hash. The server appends opt-out language when the message body lacks it, and surfaces distinct error shapes for pending approval, rate limits, and Twilio rejections.
When to use it
Useful when an assistant needs to notify a consenting US recipient by text, for example alerting someone that a long-running task finished. It suits one-off transactional notifications rather than marketing, bulk, or non-US messaging.
Requirements
Runs locally via npx (Node.js) as a stdio MCP server, desktop client only. Requires BUYER_PRIVATE_KEY, an Ethereum private key for a wallet funded on Base Sepolia with a little ETH for gas and USDC for payments. SMS_URL is optional and defaults to the seller's public endpoint. Network access is needed.
Before you install
BUYER_PRIVATE_KEY is a wallet private key that authorizes spending; use a throwaway funded wallet and keep the key out of shared configs. Every call spends $0.03 USDC, and a Twilio-side rejection still counts as a send attempt. The operator is responsible for recipient consent under TCPA rules; marketing, non-consenting, non-US, and restricted-content messages are prohibited. Message details and payment go to a third-party seller, and sends are logged for audit.

Installation

In SourceWeft

  1. Open X402 Sms in the dashboard and add it to a workspace.
  2. Enable the server for the chats that should use its tools.

Desktop only via STDIO. STDIO servers start a local process, so they need the SourceWeft desktop host.

Other MCP clients

Follow the launch instructions in the repository.

README

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 the seller's toll-free number (Twilio verification in progress)
  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 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):

json
{  "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:

Generate a throwaway key:

bash
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 varRequiredDefault
BUYER_PRIVATE_KEYyes—
SMS_URLnohttps://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.

CauseWhat you'll see in chatWas 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 guidanceno
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_secondsno
Twilio-side rejection (e.g. invalid number 21211, opted-out 21610)Friendly hint mapped from the Twilio error code + the full response bodyyes (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

Source: README.md at commit 61115a4

Tools

0
SourceWeft has not started this package in its sandbox yet, so its tools are not known.

Version history

1
  1. v0.1.0LatestSep 16, 2026

Score

40% of the applicable checks met

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  • Reached in the last 30 days25 pts

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  • Auth declared10 pts

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  • Tools listed15 pts

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  • DescriptionRequired15 pts
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  • Documentation15 pts
  • License10 pts

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