guard-x402-payments

Guard x402 Payments

Use the live IntentFence service to inspect the exact x402 quote the caller observed. Keep signing keys local and treat the result as policy evidence, not as permission to spend.

Choose the check

• For a real x402 quote, use the paid exact-quote assessment. It costs 0.005 USDC on Base per successful assessment.
• For a declared action without a PAYMENT-REQUIRED challenge, use the free, unsigned preview. Do not describe a preview as verified or settled.
• If the caller has not authorized the 0.005 USDC assessment fee, show the fee and stop before signing or submitting payment.

Assess an exact quote

1. Make the intended request without payment and capture the complete base64 PAYMENT-REQUIRED header, exact target URL, and HTTP method.
2. Define policy.max_price_usdc. Add every approved merchant address to policy.allowed_payees; without an explicit matching payee, a quote cannot receive safe_to_proceed.
3. Call the MCP tool intentfence_x402_assessment at https://agentpass-protocol.rmalka06.chatgpt.site/api/mcp, or POST the same input to https://agentpass-protocol.rmalka06.chatgpt.site/api/x402-assessments?utm_source=agent_skill&utm_medium=agent&utm_campaign=guard_x402_payments:

{
  "subject": "agent:buyer-07",
  "target_url": "https://merchant.example/paid-resource",
  "method": "GET",
  "payment_required": "BASE64_PAYMENT_REQUIRED_HEADER",
  "policy": {
    "max_price_usdc": "0.10",
    "allowed_payees": ["0x1111111111111111111111111111111111111111"]
  }
}

1. Expect IntentFence's own x402 challenge. Have the caller's x402 client sign it locally only after fee authorization, then retry the unchanged request with PAYMENT-SIGNATURE or the MCP payment metadata required by that client.
2. Accept a completed assessment only when the response is successful and includes the decision, signed receipt, and x402 settlement evidence. The service fee settlement does not prove that the merchant was paid or that it will deliver.