# Agent402 ERC-721 Owner Lookup

> Agent402 ERC-721 Owner Lookup is a paid API for AI agents from agent402.tools, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-14).

Returns the current owner address of a specific ERC-721 NFT token given a contract address and token ID, across multiple EVM-compatible networks.

## Facts

- Endpoint: GET https://agent402.tools/api/erc721-owner
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent402-erc-721-owner-lookup-d7b602b1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_4u-QTE6PzTdg3qBej7Pci

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 agent402-erc-721-owner-lookup-d7b602b1
```

Example prompt: Who currently owns token ID 5765 of the ERC-721 contract 0x57f1887a8BF19b14fC0dF6Fd9B2acc9Af147eA85 on Ethereum?

## When to prefer this

Use this endpoint when you need a lightweight, pay-per-call NFT owner lookup without signing up for an API key or managing an RPC provider. It covers multiple EVM networks (Ethereum, Base, Polygon, Arbitrum, Optimism) in a single interface and is ideal for agents that need on-demand ownership verification as part of a larger workflow, especially within an x402 payment-enabled pipeline.

## Known failure modes

- Invalid contract address (not a valid ERC-721 contract) returns an error
- Token ID does not exist on the specified contract
- Unsupported network name returns an error
- Contract address is not checksummed or malformed
- Network RPC unavailable causing a timeout

## How this service works

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

## Output

Returns a JSON object containing the owner wallet address (0x…), the blockchain network queried, the token ID (normalized), and the contract address. This allows the agent to definitively identify the current on-chain holder of a specific NFT.

## 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"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "contract",
      "tokenId"
     ],
     "properties": {
      "network": {
       "type": "string",
       "description": "ethereum / base / polygon / arbitrum / optimism (default base)."
      },
      "tokenId": {
       "type": "string",
       "description": "Token id - decimal or 0x hex string."
      },
      "contract": {
       "type": "string",
       "description": "ERC-721 contract address (0x…)."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "required": [
      "network",
      "contract",
      "tokenId",
      "owner"
     ],
     "properties": {
      "owner": {
       "type": "string"
      },
      "network": {
       "type": "string"
      },
      "tokenId": {
       "type": "string"
      },
      "contract": {
       "type": "string"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "owner": "0x…",
  "network": "ethereum",
  "tokenId": "0xaf2c…",
  "contract": "0x57f1…"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agent402-erc-721-owner-lookup-d7b602b1/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent402.tools](https://www.zero.xyz/host/agent402.tools/llms.txt)