# ERC721 ownerOf Lookup

> ERC721 ownerOf Lookup is a paid API for AI agents from ari001.tailb4ac3a.ts.net, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-02).

Returns the current owner address of a specific ERC721 NFT token by contract address and token ID on Ethereum

## Facts

- Endpoint: GET https://ari001.tailb4ac3a.ts.net/v1/ventures/ethereum_contract_abi_service/erc721_ownerof?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/erc721-ownerof-lookup-60d51e50
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_l4QO1aGrlk-VMInBqMRhv

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 erc721-ownerof-lookup-60d51e50
```

Example prompt: Who currently owns token ID 7804 on the CryptoPunks ERC721 contract at 0xb47e3cd837dDF8e4c57F05d70Ab865de6e193BBB on Ethereum?

## When to prefer this

Use this endpoint when you need to resolve the current holder of a specific ERC721 NFT on Ethereum mainnet given a contract address and token ID. Prefer this over general blockchain RPC calls when you want a simple, paid, ready-made API without managing your own node. It is specifically scoped to ERC721 ownerOf queries on Ethereum, so avoid it for ERC1155 tokens, Base chain NFTs, or bulk ownership lookups.

## Known failure modes

- Invalid contract address format returns a 400 or error response
- Token ID does not exist on the contract causes a revert / error result
- Contract address is not an ERC721 contract returns an error
- Network or RPC node unavailability causes a timeout or 5xx error
- Token ID exceeds 78 decimal digits fails schema validation

## How this service works

Returns the owner address of a specific ERC721 token by token ID. Input: contract address (string), tokenId (string). Output: owner address (string). Query: token (ERC-721 contract, 0x + 40 hex), id (token id, decimal).

## Output

Returns a JSON object with ok (boolean), the queried token contract address, token ID, and the owner field containing the Ethereum address (0x-prefixed, 40 hex chars) that currently holds the specified ERC721 token. On failure, returns ok: false with an error message.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "token",
      "id"
     ],
     "properties": {
      "id": {
       "type": "string",
       "pattern": "^[0-9]{1,78}$",
       "description": "token id, decimal"
      },
      "token": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]{40}$",
       "description": "ERC-721 contract, 0x + 40 hex"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "required": [
      "ok",
      "service"
     ],
     "properties": {
      "ok": {
       "type": "boolean"
      },
      "chain": {
       "type": "string"
      },
      "error": {
       "type": "string",
       "description": "present when ok is false"
      },
      "method": {
       "type": "string"
      },
      "result": {
       "type": "object",
       "properties": {
        "id": {
         "type": "string"
        },
        "owner": {
         "type": "string",
         "pattern": "^0x[0-9a-fA-F]{40}$"
        },
        "token": {
         "type": "string",
         "pattern": "^0x[0-9a-fA-F]{40}$"
        }
       }
      },
      "service": {
       "type": "string"
      }
     }
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/erc721-ownerof-lookup-60d51e50/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from ari001.tailb4ac3a.ts.net](https://www.zero.xyz/host/ari001.tailb4ac3a.ts.net/llms.txt)