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Behavioural 402 probe

x402 checker

Paste a paywalled resource URL. We’ll GET it with no payment header and verify it returns 402 Payment Requiredwith a valid x402 payment-requirements payload.

What is x402?

x402 reuses the long-reserved HTTP 402 Payment Required status code as a machine-readable paywall. A protected resource responds with 402 and a JSON body listing the payment options an agent can use. The agent pays, re-issues the request with an X-PAYMENT header, and receives the resource. It’s a clean replacement for API keys, OAuth handshakes, and bespoke billing flows for agent-to-resource transactions.

Why adopt it

If you’re selling API access, inference, data, or any metered resource to autonomous agents, x402 lets the agent discover the price and pay without prior account setup. No signup form, no API key rotation — just an HTTP request, a 402, a payment, and a resource. Especially useful for pay-per-call AI APIs and agent-to-agent commerce.

What we check

  • C10 — 402 Payment Required response. The URL returns HTTP 402 with a parseable JSON body containing top-level x402Version (number) and a non-empty accepts array.
  • C11 — accepts entries. Only runs when C10 passes. Each entry has a non-empty scheme. When the scheme is exact, the entry must also include network, maxAmountRequired, resource, payTo, asset, and maxTimeoutSeconds.

Minimal valid response

HTTP/1.1 402 Payment Required
Content-Type: application/json

{
  "x402Version": 1,
  "accepts": [
    {
      "scheme": "exact",
      "network": "base-sepolia",
      "maxAmountRequired": "1000",
      "resource": "https://api.example.com/v1/inference",
      "description": "One inference call",
      "mimeType": "application/json",
      "payTo": "0x0000000000000000000000000000000000000000",
      "asset": "0x036CbD53842c5426634e7929541eC2318f3dCF7e",
      "maxTimeoutSeconds": 60
    }
  ]
}

Status 402, JSON body, top-level x402Version and accepts, and a well-formed exact entry.

Specifications

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