x402 Stellar MCP Server

Local MCP server (stdio) that can call x402-protected HTTP resources and automatically pay in Stellar USDC.

Features

• Payment flow (stellar:testnet or stellar:pubnet)

• Default testnet configuration

• Mainnet-ready via env switch

• Optional OpenZeppelin facilitator auth via env

• No resource whitelist: URL is provided at tool call time

Related MCP server: x402 Payment Gateway MCP Server

Tools Exposed

• x402_wallet_info: shows active wallet address/network/config

• x402_facilitator_supported: checks configured facilitator /supported endpoint

• fetch_paid_resource: generic paid fetch (url, method, optional body/headers)

Prerequisites

• Node.js 20+

• A Stellar wallet funded with testnet XLM + testnet USDC

• x402 resource server running (your app/index.js demo)

• x402 facilitator running on http://localhost:4022

Setup

npm install
cp .env.example .env

Testnet

For testnet you'll need to run a facilitator locally on port 4022. I'd recommend using the one included in the coinbase x402 repo: https://github.com/coinbase/x402/tree/main/examples/typescript/facilitator/advanced

Update .env with your wallet key:

STELLAR_SECRET_KEY=S...
STELLAR_NETWORK=stellar:testnet

Pubnet

For mainnet you'll just need an OpenZeppelin API Key for the relayer. You can get one here (Thank you for making this easy): https://channels.openzeppelin.com/gen

STELLAR_NETWORK=stellar:pubnet
STELLAR_RPC_URL=https://rpc.lightsail.network/
X402_FACILITATOR_URL=https://channels.openzeppelin.com/x402
X402_FACILITATOR_API_KEY=<your-openzeppelin-api-key>

X402_FACILITATOR_API_KEY is optional in general, but required for OpenZeppelin channels. When set, fetch_paid_resource auto-adds Authorization: Bearer <key> for requests under X402_FACILITATOR_URL (unless you provide Authorization explicitly).

Run

npm run dev

The MCP server runs over stdio for Claude/Codex integrations.

TTS Proxy

The paid /api/tts route can use either elevenlabs or smallest. Set a default provider in .env, and optionally override it per request by sending "provider": "elevenlabs" or "provider": "smallest" in the JSON body. You can also send "provider": "auto" with a routing "priority" of "cheap", "fast", or "quality" to let the server pick a provider dynamically.

To run the real x402-protected TTS proxy, configure:

STELLAR_NETWORK=stellar:testnet
X402_FACILITATOR_URL=http://localhost:4022
TTS_PROVIDER=elevenlabs
ELEVENLABS_API_KEY=<your-elevenlabs-api-key>
ELEVENLABS_MODEL_ID=eleven_flash_v2_5
ELEVENLABS_VOICE_ID=21m00Tcm4TlvDq8ikWAM
ELEVENLABS_ESTIMATED_PRICE_USD=0.06
ELEVENLABS_ESTIMATED_LATENCY_MS=900
ELEVENLABS_QUALITY_SCORE=9.5
SMALLEST_API_KEY=<your-smallest-api-key>
SMALLEST_MODEL=lightning
SMALLEST_VOICE_ID=emily
SMALLEST_LANGUAGE=en
SMALLEST_ESTIMATED_PRICE_USD=0.03
SMALLEST_ESTIMATED_LATENCY_MS=500
SMALLEST_QUALITY_SCORE=8.3
ALLOW_SYSTEM_PROXY=false
PAY_TO_ADDRESS=<your-stellar-receiving-address>

For pubnet, also set:

STELLAR_NETWORK=stellar:pubnet
STELLAR_RPC_URL=https://rpc.lightsail.network/
X402_FACILITATOR_URL=https://channels.openzeppelin.com/x402
X402_FACILITATOR_API_KEY=<your-openzeppelin-api-key>

Then start the proxy with:

npm run start:elevenlabs

The protected route is:

POST http://localhost:3000/api/tts

Example request for automatic routing:

{
  "text": "Hello from the voice marketplace",
  "provider": "auto",
  "priority": "cheap",
  "language": "en"
}

The response includes marketplace metadata headers like:

X-TTS-Provider
X-TTS-Priority
X-TTS-Reason
X-TTS-Estimated-Price-Usd
X-TTS-Estimated-Latency-Ms
X-TTS-Quality-Score

This server now requires a real facilitator and will not fall back to a mock implementation. By default it also ignores HTTP_PROXY / HTTPS_PROXY / ALL_PROXY so upstream TTS requests go direct during local testing. Set ALLOW_SYSTEM_PROXY=true if you intentionally want to use a proxy.

Add To Claude / Codex

Use an MCP entry like (don't forget to change the path/):

Codex

codex mcp add x402-stellar -- npm --silent --prefix /absolute/path/to/x402-mcp-stellar run dev

Claude Code

claude mcp add x402-stellar -- npm --silent --prefix /absolute/path/to/x402-mcp-stellar run dev

Claude Desktop (untested)

{
  "mcpServers": {
    "x402-stellar": {
      "command": "npm",
      "args": ["--silent", "--prefix", "/absolute/path/to/x402-mcp-stellar", "run", "dev"]
    }
  }
}

This server loads .env from the project directory (/absolute/path/to/x402-mcp-stellar/.env).

Claude Usage

After loading the MCP server, you can ask:

Can you fetch the resource at http://localhost:3000/my-service, use the x402-stellar MCP server to pay for it, and print the response?

The tool call will pass that full URL at runtime; no URL allowlist or hardcoded endpoint is required in this MCP server.

Notes

• @x402/stellar is not currently published on npm, so this repo vendors the Stellar mechanism under src/stellar.

• Default testnet Soroban RPC is used automatically.

• Mainnet requires STELLAR_RPC_URL.

License

MIT