Xenarch — x402 MCP server for AI agent payments

Xenarch is a non-custodial x402 MCP server. AI agents — Claude, Cursor, LangChain, CrewAI — pay for HTTP 402—gated APIs and content with USDC micropayments on Base L2. No API keys, no subscriptions, no credit card on file. The agent wallet never needs ETH; USDC is the only token it ever holds. Payments settle on-chain: agent wallet → publisher wallet, direct. 0% Xenarch fee — there's no Xenarch contract in the money flow.

What makes Xenarch different

How it works

1. Discover    xenarch_check_gate("example.com")
               → { gated: true, accepts: [...] }

2. Pay         xenarch_pay("example.com")
               → x402-fetch signs an EIP-3009 USDC transferWithAuthorization
               → Settlement goes on-chain
               → Re-fetches the resource with proof of payment
               → { tx_hash, content }

No API keys. No signup. The agent wallet only ever needs USDC — no ETH, no gas coin of any kind. Xenarch never holds funds and there is no Xenarch contract between the agent and the publisher.

MCP tools

29 tools across three groups. Group 1 (discovery & payments) works with just a wallet. Groups 2 and 3 (control plane + merchant) manage your Xenarch account and need a SIWE session — run xenarch agent login once (see Account tools auth).

1. Discovery & payments — agent wallet only

2. Agent control plane — manage your spending agent (SIWE session)

Caps, scope, kill-switch, and API keys for the operator's agent. Privileged (loosening) operations require confirm: true; tightening is free.

3. Merchant — get paid (SIWE session)

Create and manage pay-links, see payments and subscribers, set the merchant profile. Same SIWE session as the control plane.

Account tools auth

• Payments (group 1) need a funded wallet (XENARCH_PRIVATE_KEY) and a control-plane link (XENARCH_API_TOKEN) — the official MCP refuses to pay without the token (XEN-480: an unlinked agent has no caps). A local per-call cap (XENARCH_MAX_PAYMENT_USD, default $1) applies on top of the managed per-tx / daily / monthly caps.
• Control plane + merchant (groups 2–3) need a SIWE session. Run xenarch agent login once — it writes a 7-day session_token to ~/.xenarch/config.json, which the MCP server reads automatically. Re-run when it expires, or call xenarch_agent_login directly from your client.
• Set XENARCH_API_TOKEN (an xa_live_ agent key) so xenarch_pay is enforced against your managed caps/scope and every MCP payment shows up in the dashboard receipts feed. The dashboard is free — sign in with your wallet at dash.xenarch.dev (just a signature, nothing moves) for per-tx / daily / monthly caps, scope rules, a kill switch, and full history. Without the token, xenarch_pay refuses to pay (fail-closed) so an unlinked agent can't settle uncapped. Note: the dashboard sign-in wallet is your identity — separate from the agent's local spending wallet.

Example responses

{
  "gated": true,
  "gate_id": "7f3a1b2c-9d4e-4a8b-b6f1-2c3d4e5f6a7b",
  "accepts": [
    {
      "scheme": "exact",
      "network": "base",
      "maxAmountRequired": "3000",
      "resource": "https://example.com/article",
      "payTo": "0xabc123...publisher_wallet",
      "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "maxTimeoutSeconds": 60
    }
  ],
  "seller_wallet": "0xabc123...publisher_wallet",
  "network": "base",
  "asset": "USDC"
}

{
  "success": true,
  "gate_id": "7f3a1b2c-9d4e-4a8b-b6f1-2c3d4e5f6a7b",
  "tx_hash": "0xdef456...abc789",
  "seller_wallet": "0xabc123...publisher_wallet",
  "url": "https://example.com/article",
  "wallet": "0x123...your_wallet",
  "content": "...gated content here..."
}

{
  "payments": [
    {
      "domain": "example.com",
      "amount_usd": "0.003",
      "tx_hash": "0xdef456...abc789",
      "paid_at": "2026-04-10T14:35:00Z"
    }
  ],
  "total_spent_usd": "0.003000",
  "count": 1,
  "wallet": "0x123...your_wallet"
}

HTTP 402 — the unused status code that x402 finally activates

HTTP 402 Payment Required is a status code reserved in the HTTP spec since 1997 for machine-to-machine payment. It went unused for decades because there was no open protocol for how a client should pay a 402 response.

x402 is that protocol: a server returns HTTP 402 with a signed price and payment details, the client signs a USDC micropayment on Base L2, and retries the request with proof of payment. Xenarch's MCP server automates both halves for AI agents — it reads the 402 challenge, signs the payment via x402-fetch, and replays the request, returning the on-chain tx hash plus the gated content.

Learn more: the x402 spec defines the payment handshake; pay.json (authored by Xenarch) is the companion open standard for machine-readable pricing served at /.well-known/pay.json — think robots.txt for payments.

API monetization with HTTP 402