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AISkills402: x402 Payment Header Check
x402
AISkills402: x402 Payment Header Check is a paid API for AI agents from api.aiskills402.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-17).
Parses and validates an x402 PAYMENT-SIGNATURE header value — decoding, version, authorization fields, clock window, signer lane, and optional cross-check against a PAYMENT-REQUIRED header — without transmitting it anywhere.
Price / call$0.005
Success—
StatusUnknown
How this service works
Payment Header Check API: reads an x402 PAYMENT-SIGNATURE header before you send it - base64/UTF-8/JSON, version, authorization fields, clock window, who signed (lane a or b) and, with the seller PAYMENT-REQUIRED, payTo/amount/network/asset. Nothing is sent anywhere. $0.005 USDC per check. POST JSON {payment_signature, payment_required?}; free example at https://api.aiskills402.com/v1/run/payment-header-check/example
Output
A JSON object indicating whether the header is valid, including: base64/UTF-8/JSON decoding results, x402 version, scheme, network, authorization fields (to, from, nonce, valid_after, valid_before, value_micro), clock state and skew, recovered signer address and lane (a or b), any findings with severity (e.g. long expiry window), and an optional cross-check against PAYMENT-REQUIRED fields (payTo, amount, network, asset).
Example use cases
Pre-flight payment header debug
“I'm building an x402 client and my payment keeps getting rejected — can you decode and validate this PAYMENT-SIGNATURE header value for me and tell me what's wrong with the authorization fields or clock window?”
Cross-check signature against requirements
“I have both the seller's PAYMENT-REQUIRED header and the PAYMENT-SIGNATURE I'm about to send — can you check whether my signature matches the payTo address, amount, network, and asset in the requirement?”
Audit signer lane and replay exposure
“Can you inspect this x402 PAYMENT-SIGNATURE and tell me which lane signed it, what address was recovered, and whether the validity window is dangerously long from a replay-attack perspective?”
Technical details
Endpoint
POSThttps://api.aiskills402.com/v1/run/payment-header-check?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need to validate or debug an x402 PAYMENT-SIGNATURE header before sending it, or when you want to cross-check it against a PAYMENT-REQUIRED header. It is the right choice for x402-protocol-specific header inspection, signer recovery, and clock/replay analysis. Prefer it over generic JWT or HTTP header validators when the header is specifically an x402 EIP-712 signed transfer authorization.
Side effects
- Invalid or non-base64 payment_signature returns decoding errors with ok:false
- Missing required payment_signature field returns a 400-level error
- Malformed JSON inside the decoded header returns a parsing error
- Clock skew or expired authorization detected and reported in findings
- Signature recovery failure returns a null or invalid recovered address
- Payment not settled (insufficient USDC balance) returns a 402 before processing
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| payment_required | — | Optional: the seller PAYMENT-REQUIRED header value, for a cross-check of payTo, amount, network and asset. |
| payment_signature | string | The value of the PAYMENT-SIGNATURE (or X-PAYMENT) header you are about to send. It is only read here, never sent anywhere. |
Output
Schema · Response
{
"type": "json",
"example": {
"ok": true,
"skill": "payment-header-check",
"engine": "1.0.0",
"replay": false,
"result": {
"clock": {
"now": 1792152000,
"state": "valid",
"skew_seconds": 120,
"state_with_skew": "valid",
"seconds_until_valid": 0,
"seconds_until_expiry": 6609600
},
"scheme": "exact",
"network": "eip155:8453",
"decoding": {
"json": true,
"utf8": true,
"base64": "standard",
"non_ascii": false
},
"findings": [
{
"code": "expiry_window_long",
"detail": "the authorization stays valid for another 6609600 seconds; a long window is replay exposure if the header leaks",
"severity": "info"
}
],
"signature": {
"lane": "a",
"bytes": 65,
"recovered": "0xa696565cfe3f65cdd0132a02e408c39418d8ce47",
"domain_used": {
"name": "USD Coin",
"chainId": 8453,
"version": "2",
"verifyingContract": "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913"
}
},
"x402_version": 2,
"authorization": {
"to": "0x0000000000000000000000000000000000000000",
"from": "0xa696565cFe3f65cdD0132a02e408C39418D8cE47",
"nonce": "0x5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e",
"valid_after": 0,
"value_micro": "1",
"valid_before": 1798761600
},
"vs_requirements": null
},
"receipt": {
"tx": "0x<settlement transaction>",
"settled": true
},
"refusal": null,
"input_sha256": "<sha256 of the request>"
}
}Tags
x402
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