---
title: x402 Checker
description: Behavioural validator for x402. Probe a paywalled URL and verify it returns 402 Payment Required with a valid payment-requirements payload.
last_updated: 2026-05-11
canonical_url: https://agent-ready.dev/x402-checker
---

# x402 Checker

> Behavioural validator for x402. Paste a paywalled resource URL and we'll GET it with no payment header to confirm it returns `402 Payment Required` with a valid 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 should I implement x402?

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 does the x402 validator 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 — Per-entry validation.** Each `accepts` entry has a non-empty `scheme`. For the `exact` scheme, the entry must also include `network`, `maxAmountRequired`, `resource`, `payTo`, `asset`, and `maxTimeoutSeconds`. Other schemes only need a non-empty `scheme` field.

## Minimal valid response

```json
{
  "x402Version": 1,
  "accepts": [
    {
      "scheme": "exact",
      "network": "base",
      "maxAmountRequired": "10000",
      "resource": "https://api.acme.dev/v1/inference",
      "payTo": "0xacme...",
      "asset": "USDC",
      "maxTimeoutSeconds": 300
    }
  ]
}
```

## Specifications

- [x402.org](https://www.x402.org) — protocol home
- [x402 whitepaper](https://www.x402.org/x402-whitepaper.pdf)
- [docs.x402.org](https://docs.x402.org/introduction)

---

Probe your paywalled resource: <https://agent-ready.dev/x402-checker>

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