# Base ERC-721 Owner Lookup

> Base ERC-721 Owner Lookup is a paid API for AI agents from api.arysphere.com, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-17).

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

## Facts

- Endpoint: GET https://api.arysphere.com/v1/ventures/x402_chain_reads_v1/base_erc721_ownerof?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-17
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/base-erc-721-owner-lookup-ee5fadb5
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_YApFy_9QlB0QWwsh0pDif

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-ee5fadb5
```

Example prompt: Who currently owns token ID 5256424 on the Base NFT contract 0xa990c6a764b73bf43cee5bb40339c3322fb9d55f?

## When to prefer this

Choose this endpoint when you need to resolve the current on-chain owner of a specific ERC-721 NFT on the Base L2 network. Prefer this over Ethereum ERC-721 lookups when the NFT collection is deployed on Base (not Ethereum mainnet). Useful for ownership verification, access gating, post-sale tracking, or any workflow where knowing the current holder wallet address is required.

## Known failure modes

- Invalid contract address format (not 0x + 40 hex) returns a 400-level error
- Token ID that does not exist on the contract may return a revert or null owner
- Contract address is not an ERC-721 contract — call will fail or return unexpected data
- Network issues reaching Base RPC may cause timeout or 5xx error
- Token ID provided as non-decimal string may fail validation

## How this service works

ARYSPHERE sells AI-written verdicts on Base token contracts (a grade, a one-liner, a roast and the contract's facts) and Base/Ethereum chain reads, paid per call in USDC on Base over x402 v2. No account and no API key.

## Output

A JSON object containing: ok (boolean success flag), chain ('base'), method ('ownerOf'), and a result object with the token's id, the owner wallet address, and the contract token address. Returns the exact on-chain ownerOf() response for the given token ID.

## 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"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "chain": "base",
  "method": "ownerOf",
  "result": {
   "id": "5256424",
   "owner": "0x456979e89917f4dc1e86662fcdfd4c9766c6684d",
   "token": "0xa990c6a764b73bf43cee5bb40339c3322fb9d55f"
  },
  "service": "x402_chain_reads_v1.base_erc721_ownerof"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/base-erc-721-owner-lookup-ee5fadb5/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.arysphere.com](https://www.zero.xyz/host/api.arysphere.com/llms.txt)