# EVM Nonce Replace Check

> 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.

## Facts

- Endpoint: POST https://api.delx.ai/api/v1/x402/evm-nonce-replace-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/evm-nonce-replace-check-406149c6
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_irQwTw6FLiPbuNzgYz4XN

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 evm-nonce-replace-check-406149c6 -d '<json body>'
```

Example prompt: Before I submit my next Ethereum transaction, check if proposed nonce 11 would replace any of these pending nonces [8, 9, 10, 11] in my queue.

## When to prefer this

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.

## Known failure modes

- 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

## 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).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "pending_nonces": {
   "type": "array",
   "items": {
    "type": "integer"
   },
   "maxItems": 256,
   "description": "Pending Nonces supplied to EVM Nonce Replace Check; used only for this bounded calculation and processed in memory without retention."
  },
  "proposed_nonce": {
   "type": "integer",
   "description": "Proposed Nonce supplied to EVM Nonce Replace Check; used only for this bounded calculation and processed in memory without retention."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "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"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/evm-nonce-replace-check-406149c6/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.delx.ai](https://www.zero.xyz/host/api.delx.ai/llms.txt)