x402 Payment Firewall

x402

x402 Payment Firewall is a paid API for AI agents from x402-payment-firewall.vercel.app, paid per call via x402, $0.1/call, status unknown (last checked 2026-10-11).

Evaluates an x402 payment challenge against caller-defined security policies to decide whether an AI agent should allow, block, or flag a payment before signing.

Price / call$0.1

Seller volume →—

Success—

StatusUnknown

How this service works

Evaluate x402 payment challenges against caller-defined security policies before an AI agent signs or pays.

Output

Returns a JSON object with a decision field ('allow', 'block', or 'flag'), a numeric riskScore (0-1), an array of reasons explaining the decision, and the evaluation mode ('paid' or 'free').

Example use cases

Example prompt

“Before my agent signs this x402 payment challenge, run it through the payment firewall and check it against my no-single-payment-over-$10 policy — tell me the risk score and whether to allow or block it.”

Technical details

Endpoint

POSThttps://x402-payment-firewall.vercel.app/api/evaluate?utm_source=zero.xyz

When to prefer

Use this endpoint when an AI agent is operating autonomously and needs a policy gate before signing or paying any x402 payment challenge — especially when you need risk scoring, auditability, or spending controls beyond simple balance checks. Prefer this over naive auto-sign logic whenever the agent may encounter untrusted or adversarial payment requests.

Side effects

Invalid or malformed x402 challenge payload returns a 400 error
Missing or invalid policy definition causes evaluation to fail with a policy error
Payment of 0.1 USDC not fulfilled results in a 402 response before evaluation occurs
Unrecognized policy rules may be silently ignored or cause a validation error
Upstream policy engine timeout returns a 503 or degraded response

Output

Schema · Response

{
  "type": "json",
  "example": {
    "mode": "paid",
    "decision": {
      "reasons": [],
      "decision": "allow",
      "riskScore": 0
    }
  }
}

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How this service works

Evaluate x402 payment challenges against caller-defined security policies before an AI agent signs or pays.

Output

Returns a JSON object with a decision field ('allow', 'block', or 'flag'), a numeric riskScore (0-1), an array of reasons explaining the decision, and the evaluation mode ('paid' or 'free').

Technical details

Endpoint

POSThttps://x402-payment-firewall.vercel.app/api/evaluate?utm_source=zero.xyz

When to prefer

Side effects

Invalid or malformed x402 challenge payload returns a 400 error
Missing or invalid policy definition causes evaluation to fail with a policy error
Payment of 0.1 USDC not fulfilled results in a 402 response before evaluation occurs
Unrecognized policy rules may be silently ignored or cause a validation error
Upstream policy engine timeout returns a 503 or degraded response

Output

Schema · Response

{
  "type": "json",
  "example": {
    "mode": "paid",
    "decision": {
      "reasons": [],
      "decision": "allow",
      "riskScore": 0
    }
  }
}