X402 Payagent MCP

@arispay/payagent-mcp

One coherent USDC payment product for AI agents: call x402-paid APIs, with spend mandates, receipts, and idempotency. Works with Claude Desktop, Cursor, Windsurf, or any MCP client. A thin wrapper around the payagent SDK.

Two ways to hold the wallet:

• Local key (zero signup). Set PAYAGENT_PRIVATE_KEY to a funded EOA key. pay signs EIP-3009 locally — no ArisPay account, no email. The only guardrail is the wallet balance; use a dedicated low-balance wallet.
• Delegated custody (managed, recommended). setup({ email }) self-provisions an account, a CDP-managed wallet, and a spend mandate in one call. ArisPay enforces per-transaction, daily, and monthly limits server-side before signing; no private key ever lives in this process.

Tools

Seven core tools (the default surface):

Wallet administration (create_agent, fund_agent, list_agents, rename_agent) loads only when the host config sets PAYAGENT_MCP_PROFILE=admin.

Every tool declares MCP safety annotations (readOnlyHint, destructiveHint, idempotentHint, openWorldHint); pay and check_payment_signal are the only destructive tools — both spend real money.

Support matrix

Notes:

• All prices are quoted by sellers in the 402 challenge; pay prefers an EVM variant and falls back to Solana when the seller offers no EVM option.
• Delegated mandates are integer cents, validated server-side before any signature exists. Local mode has no server-side cap.
• Settlement is a single on-chain transferWithAuthorization (EIP-3009): it succeeds or reverts atomically. When the seller returns X-PAYMENT-RESPONSE, the receipt carries the settlement transaction hash.
• ArisPay's own facilitator (facilitator.arispay.app) charges no facilitator fee; sellers may use any facilitator, and their fee/finality policy applies.

Setup

Add the server to your MCP client config. No environment variables are required — pick a wallet mode later, from inside the chat, or set one of the env options below.

Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json:

{

"mcpServers": { "arispay": { "command": "npx", "args": ["-y", "@arispay/payagent-mcp"] } } }

For the zero-signup mode, add the key to the env block:

      "env": { "PAYAGENT_PRIVATE_KEY": "0x..." }

Cursor

Same server block in .cursor/mcp.json. Windsurf: same pattern in ~/.codeium/windsurf/mcp_config.json.

Cold start, from nothing

• Zero signup: generate a key with npx payagent wallet new, put it in the host config as PAYAGENT_PRIVATE_KEY, send USDC on Base to the printed address. balance shows the deposit address; pay pays.
• Managed: ask the agent to run setup({ email: "you@example.com" }) — it returns the wallet address and mandate. Fund the wallet with USDC, confirm with balance, then pay. Credentials persist to ~/.payagent/config.json and are shared with the payagent CLI.

Environment variables (all optional)

Migrating from v3

v4 is a breaking release: the surface collapsed to one x402/USDC product.

Receipts and idempotency

pay requires a caller-chosen idempotencyKey (min 8 chars — use a UUID). Every completed payment writes a machine-readable receipt (amount, asset, network, wallet, settlement tx, remaining mandate) to ~/.payagent/mcp-receipts.json. Re-calling pay with a key that already paid returns the stored receipt and does not pay again — including when the paid request failed mid-flight. history lists receipts in self-custody mode; delegated mode reads the authoritative server feed.

How it works

1. The agent calls pay with a URL and an idempotencyKey; the seller answers HTTP 402 with its price.
2. With PAYAGENT_PRIVATE_KEY set, payagent signs the EIP-3009 authorization locally. Otherwise ArisPay validates the request against the agent's mandate and signs via Coinbase CDP.
3. payagent retries with the signed payment header; the seller's facilitator settles USDC on-chain.
4. The tool returns the paid response plus a structured receipt.

In delegated mode, no private key lives in this process and payments that breach the mandate are rejected before any on-chain action. In local mode, the key is yours and stays in your process.

Install

npm install @arispay/payagent-mcp

Or invoke directly via npx @arispay/payagent-mcp from an MCP client config — no pre-install required. npx buyforme-mcp is the same server under the consumer brand.

Related

• payagent — the SDK + CLI for programmatic use
• facilitator.arispay.app — ArisPay's open x402 facilitator, where paid 402s settle
• x402 protocol — HTTP 402 payment standard

License

MIT