NFT owner lookup (ERC-721 ownerOf)

Who owns this NFT? Calls ownerOf(tokenId) on any ERC-721 contract on Ethereum, Base, Polygon, Arbitrum, or Optimism. Complements nft-holdings (which lists a WALLET's NFTs) - this answers by TOKEN. Keyless multi-endpoint failover. ?contract=0x…&tokenId=123&network=ethereum

Input

Example output

{
  "network": "ethereum",
  "contract": "0x57f1…",
  "tokenId": "0xaf2c…",
  "owner": "0x…"
}

Try it - see the 402 challenge (free)

curl -i "https://agent402.tools/api/erc721-owner?contract=0x57f1887a8BF19b14fC0dF6Fd9B2acc9Af147eA85&tokenId=0xaf2caa1c2ca1d027f1ac823b529d0a67cd144264b2789fa2ea4d63a67c7103cc&network=ethereum"

The response is HTTP 402 Payment Required with exact payment requirements. Any x402 v2 client pays automatically and retries:

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/erc721-owner?contract=0x57f1887a8BF19b14fC0dF6Fd9B2acc9Af147eA85&tokenId=0xaf2caa1c2ca1d027f1ac823b529d0a67cd144264b2789fa2ea4d63a67c7103cc&network=ethereum");

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