# ERC-721 Balance Checker (Multi-Chain)

> ERC-721 Balance Checker (Multi-Chain) is a paid API for AI agents from biosfera.46-62-215-147.sslip.io, paid per call via x402, $0.001/call, status down (last checked 2026-10-02).

Returns the number of ERC-721 NFTs a wallet address holds in a given collection on Base, Ethereum, Arbitrum, Optimism, or Polygon.

## Facts

- Endpoint: GET https://biosfera.46-62-215-147.sslip.io/o/erc721-balance?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: down
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/erc-721-balance-checker-multi-chain-3928ada3
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_mDbpi7Ws9GZNjTZqTqHvv

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 erc-721-balance-checker-multi-chain-3928ada3
```

Example prompt: How many NFTs does the wallet 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045 hold in the ERC-721 collection at contract 0xBC4CA0EdA7647A8aB7C2061c2E118A18a936f13d on Ethereum?

## When to prefer this

Use this endpoint when you need to know the raw NFT count a wallet holds in a specific ERC-721 collection across the five supported chains (Base, Ethereum, Arbitrum, Optimism, Polygon). Prefer this over general NFT portfolio APIs when you already know the contract address and just need the balanceOf result without extra metadata overhead.

## Known failure modes

- Invalid wallet or contract address format (must be 0x + 40 hex chars)
- Unsupported chain value outside of base/ethereum/arbitrum/optimism/polygon
- Contract address is not a valid ERC-721 contract on the specified chain
- Network congestion or RPC node unavailability causing timeout
- Payment failure due to insufficient USDC balance for x402 micropayment

## How this service works

Use when you need how many tokens of an ERC-721 collection an address holds on Base, Ethereum, Arbitrum, Optimism or Polygon, via balanceOf, with the collection name.

## Output

Returns the NFT token count (integer balance) for the specified wallet address in the given ERC-721 contract on the requested chain, along with the collection name.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "chain",
      "contract",
      "address"
     ],
     "properties": {
      "chain": {
       "enum": [
        "base",
        "ethereum",
        "arbitrum",
        "optimism",
        "polygon"
       ],
       "type": "string"
      },
      "address": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$"
      },
      "contract": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$"
      }
     },
     "additionalProperties": false
    }
   },
   "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/erc-721-balance-checker-multi-chain-3928ada3/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from biosfera.46-62-215-147.sslip.io](https://www.zero.xyz/host/biosfera.46-62-215-147.sslip.io/llms.txt)