# OneSource Ethereum Transaction Nonce Lookup

> OneSource Ethereum Transaction Nonce Lookup is a paid API for AI agents from api.onesource.io, paid per call via x402, $0.003/call, status unknown (last checked 2026-09-15).

Returns the next transaction nonce (transaction count) for any Ethereum wallet address via eth_getTransactionCount

## Facts

- Endpoint: GET https://api.onesource.io/api/chain/nonce/:address
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/onesource-ethereum-transaction-nonce-lookup-3b274c2d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_eSE7LJnkxbn1Zk6c5-OIj

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 onesource-ethereum-transaction-nonce-lookup-3b274c2d
```

Example prompt: What's the next nonce for Ethereum wallet 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045 on mainnet — I need to know how many transactions it has sent so I can sign my next transaction correctly.

## When to prefer this

Use this endpoint when you need to determine the correct nonce for constructing and signing a new Ethereum transaction, or when you need to audit how many transactions a wallet has sent. Useful for transaction sequencing, replay protection, and wallet activity checks. Supports both mainnet and Sepolia testnet, and allows querying at specific historical blocks for forensic or analytical purposes.

## Known failure modes

- Invalid Ethereum address format (not 0x + 40 hex chars) — returns validation error
- Unknown network value other than 'ethereum' or 'sepolia' — returns error
- Invalid block parameter format — returns validation error
- Node RPC timeout or upstream Ethereum node unavailability — returns 5xx error
- Payment failure (x402) — returns 402 Payment Required

## How this service works

Next transaction nonce for any Ethereum wallet via eth_getTransactionCount - how many txs it has sent

## Output

Returns the transaction nonce (count of transactions sent) for the specified Ethereum address, representing the next nonce to use when constructing a new transaction. Can be queried at a specific block number, block tag (latest, pending, earliest, safe, finalized), or hex block reference.

## Example request

```json
{
 "block": "latest",
 "address": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
 "network": "ethereum"
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/onesource-ethereum-transaction-nonce-lookup-3b274c2d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.onesource.io](https://www.zero.xyz/host/api.onesource.io/llms.txt)