null-402-mcp

An MCP server that lets any agent pay x402 APIs privately on Stellar. Plug it into Claude (Desktop / Code) or any MCP client and your agent can create a wallet, deposit into the null-402 privacy pool, and pay x402-protected endpoints with a zero-knowledge proof — revealing only a nullifier, never the wallet, amount, or endpoint.

Tools

Related MCP server: payments-gateway

Plug into Claude

claude_desktop_config.json (or Claude Code MCP config):

{
  "mcpServers": {
    "null-402": {
      "command": "node",
      "args": ["/ABS/PATH/null-402-mcp/src/index.mjs"],
      "env": { "NULL402_WALLET": "/ABS/PATH/.null-402/wallet.json" }
    }
  }
}

Then ask Claude: “deposit 1 XLM, then pay https://…/v1/price/BTC privately and tell me the price.”

Prerequisites

(cd ../null-402-circuits && npm install && npm run build)   # proving artifacts
(cd ../null-402-sdk      && npm install && npm run build)   # SDK → dist
(cd ../null-402-gateway  && npm install && npm run build)   # gateway → dist
npm install

🤖 Autonomous agent demo (Groq)

A Groq LLM, given the null-402 MCP tools, autonomously sets up a wallet, deposits a note, and pays an x402 API privately:

GROQ_API_KEY=…  NULL402_PROVIDER=$(stellar keys address null402)  npm run agent

Real run (llama-3.3-70b-versatile):

🤖 Groq agent + null-402 MCP
  MCP tools: create_wallet, wallet_status, deposit, pay
  paid API: http://localhost:52138/v1/price/BTC

  → agent calls create_wallet({})
      Created + funded a Stellar testnet wallet: GDMCK3XD…44EC
  → agent calls deposit({})
      Deposited a 1-XLM note. deposit tx: 0ad8a31135a26c329e0479e45c8ca8a18287b0a0121fe0a3cbb3b9669f082c0d
  → agent calls pay({"url":"http://localhost:…/v1/price/BTC"})
      Paid privately — HTTP 200, X-Privacy=zk-groth16.
      The only thing revealed on-chain: nullifier 139508983317078515095272…
      settled on-chain (1 XLM → provider): 3969f955df784adb01a49665dab84122cacbbad448585a70dacd06b9117fea2b
      API response: { … "price": 52406.13 … }

  💬 agent answer: The current BTC price is $52,406.13.

• deposit: https://stellar.expert/explorer/testnet/tx/0ad8a31135a26c329e0479e45c8ca8a18287b0a0121fe0a3cbb3b9669f082c0d

• settle (verify → pay provider 1 XLM, on-chain): https://stellar.expert/explorer/testnet/tx/3969f955df784adb01a49665dab84122cacbbad448585a70dacd06b9117fea2b

The deposit is public; the payment + settlement reveal only a nullifier — not which agent paid, how much, or which endpoint.

Self-test (no LLM)

Exercises the tool logic against a real local gateway + the deployed testnet contracts:

NULL402_PROVIDER=$(stellar keys address null402) npm run selftest

[create_wallet] Created + funded: GCOABGVQ…OAYV
[deposit]       deposit tx: 5130128fe295a35441d27fea10b47a51f4f5df92c30f2cff0286c30aceafee10
[pay + settle]  Paid privately — HTTP 200, X-Privacy=zk-groth16.
                settled on-chain (1 XLM → provider): f551e134a0dcdf3fd85695bf867313d59a4317a302f94d3f4c7a35911545be25
                API response: { … "price": 52797.80 … }
OK - MCP tools work end-to-end (real deposit + private x402 pay + on-chain settle).

How pay works

1. GET url → 402 with the payment terms (payTo, price).

2. Pick an unspent note → generate a real Groth16 proof bound to (gateway, price, request) — locally, secrets never leave.

3. Retry with X-PAYMENT: <proof> → the gateway verifies the proof on-chain (Soroban BN254 pairing) → 200 + the API response.

4. The gateway operator settles on-chain: pool.settle re-runs the pairing check, spends the nullifier, and pays the provider 1 XLM from the pool. The settle tx is returned in X-Settle-Tx.

Notes are a fixed 1-XLM denomination, so the operator settles an exact amount without learning anything about the note — preserving the privacy of the spend. (Settlement here is synchronous for the demo; a production gateway would batch it.)

Deployed testnet contracts (defaults; override via NULL402_POOL / NULL402_VERIFIER):

Wallets are stored locally (NULL402_WALLET) and never committed. This is a testnet demo — don't put real funds in the file-based wallet.