# x402 Payment Challenge Inspector

> x402 Payment Challenge Inspector is a paid API for AI agents from sentinel.rootstuff.io, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-15).

Fetches and returns the 402 payment challenge (payment envelope) from a paid HTTP endpoint without actually paying it

## Facts

- Endpoint: GET https://sentinel.rootstuff.io/x402/payment-envelope
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-payment-challenge-inspector-74c262f6
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_xBJDerr_7u3KSKx4t1vaY

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability x402-payment-challenge-inspector-74c262f6
```

Example prompt: Probe https://api.example.com/premium-data and pull back its x402 payment challenge so I can see the pay-to address, network, and required amount without actually paying.

## When to prefer this

Use this endpoint when you need to inspect or validate an x402 payment challenge from a paid HTTP endpoint before committing to payment — especially useful for debugging payment flows, verifying pay-to addresses and networks, discovering endpoint pricing, or building x402-aware agents that need to parse challenge parameters dynamically. Prefer this over manually sending HTTP requests when you want a structured, parsed result with optional validation against expected values.

## Known failure modes

- Target URL does not return a 402 status (not a paid endpoint)
- Target URL is unreachable or times out
- Malformed or non-standard x402 challenge returned by target
- Expected pay-to address, network, or amount does not match — validation mismatch returned
- Invalid URL format provided as input

## How this service works

Read a paid endpoint's 402 challenge without paying it

## Output

Returns the raw x402 payment envelope from the target URL, including the pay-to wallet address, CAIP-2 network identifier, required payment amount in USD, and any other challenge fields — all without executing a payment. May include validation results if expected values were supplied.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "description": "The paid http(s) route to probe."
  },
  "expected_pay_to": {
   "type": "string",
   "description": "Optional. Address the challenge should pay to."
  },
  "expected_network": {
   "type": "string",
   "description": "Optional. CAIP-2 network such as eip155:8453."
  },
  "expected_amount_usd": {
   "type": "string",
   "description": "Optional. Price in USD the challenge should carry."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-payment-challenge-inspector-74c262f6/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from sentinel.rootstuff.io](https://www.zero.xyz/host/sentinel.rootstuff.io/llms.txt)