# Base ERC-721 Owner Lookup

> Base ERC-721 Owner 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 2026-10-10).

Returns the current owner address of a specific ERC-721 NFT token on the Base blockchain by calling ownerOf(id) on the contract.

## Facts

- Endpoint: GET https://ari001.tailb4ac3a.ts.net/v1/ventures/x402_chain_reads_v1/base_erc721_ownerof?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-10
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/base-erc-721-owner-lookup-337da17b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_-Dhq6eUO4V_2irvnC2Ii9

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 base-erc-721-owner-lookup-337da17b
```

Example prompt: Who currently owns token ID 1337 on the ERC-721 contract 0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48 on Base?

## When to prefer this

Use this endpoint when you need to resolve the current owner of a specific ERC-721 NFT on the Base blockchain. Prefer this over generic RPC calls when you want a simple, paid-per-call abstraction that handles the eth_call to ownerOf without managing your own Base node connection. Particularly useful for agents verifying NFT-gated access, tracking provenance, or enriching NFT metadata with live ownership data on Base specifically (not Ethereum mainnet or other chains).

## Known failure modes

- Invalid contract address format (not 0x + 40 hex) — returns 400 or validation error
- Token ID does not exist on the contract — contract may revert, resulting in an error response
- Contract address is not an ERC-721 contract — call may fail or return unexpected data
- Base chain node unavailability — returns a 5xx error
- Token ID provided in non-decimal format — query may fail or return incorrect results

## How this service works

NFT owner read on Base: takes token (ERC-721 contract, 0x + 40 hex) and id (decimal token id) and returns the address that ownerOf(id) reports on the contract.

## Output

Returns the Ethereum address (0x + 40 hex characters) that the ERC-721 contract's ownerOf(id) function reports as the current holder of the specified token ID on the Base chain.

## Request schema (JSON Schema)

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

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/base-erc-721-owner-lookup-337da17b/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)