# Base Onchain Data - Address Inspector

> Base Onchain Data - Address Inspector is a paid API for AI agents from onchaincheck.dev, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-29).

Identifies what lives at a Base blockchain address: EOA wallet, smart contract type, token standard (ERC-20/721/1155), name, symbol, proxy info, bytecode size, nonce, and ETH balance.

## Facts

- Endpoint: GET https://onchaincheck.dev/base/contract?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/base-onchain-data-address-inspector-eb534bf8
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_hRpgxN4244WcMQ-a4Yy-r

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-onchain-data-address-inspector-eb534bf8
```

Example prompt: Can you tell me what's at Base address 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 — is it a wallet or a contract, and if it's a token what standard does it use, its name and symbol, and whether it's an upgradeable proxy?

## When to prefer this

Choose this endpoint when you need a comprehensive one-shot classification of any Base address — whether it's a wallet or contract, what token standard it implements, proxy admin/implementation details, and current ETH balance. Prefer it over generic block explorers when you need structured, machine-readable output suitable for agent pipelines. Use it for due diligence before DeFi interactions, verifying token contracts, or resolving unknown addresses on Base specifically (not Ethereum mainnet or other L2s).

## Known failure modes

- Invalid address format (not a 42-character 0x hex string) — likely 400 error
- Address not found or zero activity on Base — may return minimal data
- Proxy detection may be incomplete for non-standard proxy patterns
- RPC timeout or Base node unavailability — service error
- Payment failure via x402 protocol — 402 response if USDC balance insufficient

## How this service works

Identify what lives at a Base address: wallet (EOA, including EIP-7702 delegation) or contract, which token standard it implements (ERC-20, ERC-721, ERC-1155), name and symbol, upgradeable-proxy implementation and admin, smart-wallet proxies, bytecode size, nonce and ETH balance.

## Output

Returns a JSON object with: address, chain ('base'), kind (e.g. 'ERC-20 token', 'EOA', 'smart contract'), name, symbol, decimals, totalSupply, nativeBalance (ETH), bytecodeBytes, nonce, isContract flag, standards object (erc20/erc165/erc721/erc1155 booleans), and proxy details (upgradeable boolean, implementation address, admin address) when applicable.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "address"
     ],
     "properties": {
      "address": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "Any address on Base"
      }
     },
     "additionalProperties": false
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "kind": "ERC-20 token",
  "name": "USD Coin",
  "chain": "base",
  "proxy": {
   "admin": "0x4fc7850364958d97B4d3f5A08f79db2493f8cA44",
   "upgradeable": true,
   "implementation": "0x2Ce6311ddAE708829bc0784C967b7d77D19FD779"
  },
  "symbol": "USDC",
  "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "decimals": 6,
  "standards": {
   "erc20": true,
   "erc165": false,
   "erc721": false,
   "erc1155": false
  },
  "isContract": true,
  "totalSupply": "4291989037.45169",
  "bytecodeBytes": 1852,
  "nativeBalance": "0.009800646158085843"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/base-onchain-data-address-inspector-eb534bf8/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from onchaincheck.dev](https://www.zero.xyz/host/onchaincheck.dev/llms.txt)