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EVM Nonce Replace Check
x402
EVM Nonce Replace Check is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).
Checks whether a proposed EVM transaction nonce targets any pending nonces in a list, enabling pre-flight nonce replacement safety validation.
Price / call$0.001
Success—
StatusUnknown
How this service works
EVM Nonce Replace Check: EVM Nonce Replace Check checks whether a proposed nonce targets a caller-supplied pending nonce from bounded caller-supplied values without an external provider. Call EVM Nonce Replace Check before signing, submitting, replacing, or accepting an EVM/Base transaction assembled from caller-owned data. Returns normalized transaction evidence, calculated budget or shape findings, and a fail-closed preflight status for EVM Nonce Replace Check as versioned deterministic JSON.…
Output
Returns a JSON object with the proposed nonce value, a boolean flag (targets_pending) indicating whether it matches any pending nonce, the operation name (evm_preflight:evm_nonce_replace_check), pass/fail status, and evidence metadata including input hash, retention status (always false), and external call count (always 0).
Example use cases
Pre-flight nonce check before transaction broadcast
“I'm about to broadcast an EVM transaction with nonce 42 — can you check if that nonce would replace any of the currently pending nonces [40, 41, 42, 43] in my wallet queue before I send it?”
Agent transaction queue conflict detection
“My autonomous trading agent has pending nonces [5, 6, 7] queued up. Check whether using proposed nonce 6 would collide and replace one of those pending transactions.”
Nonce safety validation for gas bump retry
“I'm trying to speed up a stuck transaction by resubmitting with nonce 15. My pending nonces are [14, 15, 16] — verify whether nonce 15 is actually targeting a pending transaction before I proceed.”
Technical details
Endpoint
POSThttps://api.delx.ai/api/v1/x402/evm-nonce-replace-checkWhen to prefer
Use this endpoint when an AI agent or automated system needs to verify whether a proposed EVM transaction nonce would replace an existing pending transaction before submission, especially in high-throughput or automated transaction pipelines where nonce collisions can cause unintended transaction replacement. Prefer this over manual nonce management when building safe transaction queues or retry logic for stuck transactions.
Side effects
- Invalid pending_nonces array (non-integer elements or exceeds 256 item limit) returns validation error
- Missing required proposed_nonce field returns schema error
- Malformed JSON body returns 400 bad request
- Payment not included or invalid x402 payment header returns 402 Payment Required
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| pending_nonces | array | Pending Nonces supplied to EVM Nonce Replace Check; used only for this bounded calculation and processed in memory without retention. |
| proposed_nonce | integer | Proposed Nonce supplied to EVM Nonce Replace Check; used only for this bounded calculation and processed in memory without retention. |
Output
Schema · Response
{
"type": "json",
"example": {
"result": {
"proposed_nonce": 11,
"targets_pending": true
},
"schema": "delx/util-evm-nonce-replace-check/v1",
"status": "pass",
"evidence": {
"retained": false,
"input_sha256": "a3ab4cbc105327ec6bf99174fcfd83de2a8605ff927d8cd849aed39cba23d03e",
"external_calls": 0
},
"operation": "evm_preflight:evm_nonce_replace_check"
}
}Tags
x402
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