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X402 Payment Nonce Check
x402
X402 Payment Nonce Check is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-20).
Validates a payment nonce for presence, minimum length, and caller-known reuse against a bounded list of previously seen nonces, returning acceptance or rejection status with mismatch reasons.
Price / call$0.001
Success—
StatusUnknown
How this service works
X402 Payment Nonce Check: X402 Payment Nonce Check checks a payment nonce for presence, length, and caller-known reuse from bounded caller-supplied values without an external provider. Call X402 Payment Nonce Check before paying for or accepting an x402 or agent delivery assembled from caller-supplied challenge and result metadata. Returns contract-specific checks, normalized evidence, mismatch reasons, and an explicit acceptance or rejection status for X402 Payment Nonce Check as versioned det…
Output
Returns a structured verdict including an explicit acceptance or rejection status, contract-specific check results (presence, length conformance, reuse detection), normalized evidence of the checks performed, and mismatch reasons explaining any failures — all deterministically computed in memory without external calls or data retention.
Example use cases
Replay attack prevention before payment
“I'm about to accept an x402 payment with nonce 'nonce-a8f3d92b'; check if it's at least 32 characters long and verify it's not already in my seen-nonces list: ['nonce-111aaa', 'nonce-222bbb', 'nonce-333ccc'].”
Agent delivery nonce pre-flight check
“Before I finalize this agent delivery result, validate the nonce 'delivery-nonce-zx9q2m' — minimum length 20 — and make sure it's not a duplicate of any of these previously used nonces: ['delivery-nonce-aaa1', 'delivery-nonce-bbb2'].”
Nonce presence and format gate
“Can you run a nonce check on 'pay-7f3a' with a minimum length of 8 against an empty seen-nonces list, so I can confirm whether this nonce passes basic validity before forwarding the payment?”
Technical details
Endpoint
POSThttps://api.delx.ai/api/v1/x402/x402-payment-nonce-check?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need a lightweight, stateless, in-memory nonce validation step before accepting or paying for an x402 payment or agent delivery — especially when you maintain your own seen-nonces list on the caller side and want deterministic, contract-specific rejection reasons without an external database or provider dependency. Prefer it over custom nonce logic when you need normalized evidence and versioned results for audit trails.
Side effects
- Nonce absent or empty string — rejected with presence failure reason
- Nonce shorter than minimum_length — rejected with length mismatch reason
- Nonce found in seen_nonces list — rejected with reuse/replay detection reason
- seen_nonces array exceeds 256 items — request may be rejected or truncated
- nonce or seen_nonces values exceed 8192 character limit — validation error
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| nonce | string | Nonce supplied to X402 Payment Nonce Check; used only for this bounded calculation and processed in memory without retention. |
| seen_nonces | array | Seen Nonces supplied to X402 Payment Nonce Check; used only for this bounded calculation and processed in memory without retention. |
| minimum_length | integer | Minimum Length supplied to X402 Payment Nonce Check; used only for this bounded calculation and processed in memory without retention. |
Output
Schema · Response
{
"type": "json",
"example": {
"result": {
"reused": false,
"accepted": true,
"nonce_length": 18
},
"schema": "delx/util-x402-payment-nonce-check/v1",
"status": "pass",
"evidence": {
"retained": false,
"input_sha256": "5b10e7096699f6b6a1dcbc3414bdd28a9a8deeb87ccf9e505917b2a855abe5e2",
"external_calls": 0
},
"operation": "delivery_contract:x402_payment_nonce_check"
}
}Tags
x402
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