# Base Mainnet ERC-20 Token Balance Lookup

> Base Mainnet ERC-20 Token Balance Lookup is a paid API for AI agents from x402-data-api.sigrunner.workers.dev, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-16).

Returns the ERC-20 token balance for a given holder address on Base mainnet, including token symbol, decimals, and human-readable formatted balance.

## Facts

- Endpoint: GET https://x402-data-api.sigrunner.workers.dev/chain/token-balance
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/base-mainnet-erc-20-token-balance-lookup-88860933
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_PhhKKhvThG0fcDnEPhjg-

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-mainnet-erc-20-token-balance-lookup-88860933
```

Example prompt: What's the USDC balance (contract 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48) for wallet 0x742d35Cc6634C0532925a3b8D4C9b3C7e8Cb5f3 on Base mainnet, and show me the formatted amount with symbol?

## When to prefer this

Use this endpoint when you need the ERC-20 token balance (not ETH) of a specific wallet on Base mainnet, especially when you also need human-readable formatting with symbol and decimals. Prefer this over the ETH balance endpoint when querying ERC-20 tokens specifically. Use the wallet bundle endpoint if you need ETH balance alongside other wallet data in one call.

## Known failure modes

- Invalid or non-0x-prefixed contract address returns an error or empty response
- Non-existent ERC-20 contract address (EOA or zero balance contract) may return zero or an error
- Invalid holder address format causes a 400-level error
- Address with no holdings returns balance of 0
- Network or RPC issues on Base mainnet may cause timeouts
- Payment not included or insufficient results in 402 Payment Required

## How this service works

ERC-20 token balance of a Base mainnet address, incl. symbol, decimals, balance_formatted.

## Output

A JSON object containing the raw token balance, a human-readable formatted balance (adjusted for decimals), the token symbol, and the number of decimals for the ERC-20 contract on Base mainnet.

## 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",
     "properties": {
      "token": {
       "type": "string",
       "description": "0x-prefixed 20-byte ERC-20 contract address"
      },
      "address": {
       "type": "string",
       "description": "0x-prefixed 20-byte holder address"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "chain": "base",
  "token": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "symbol": "USDC",
  "address": "0x4200000000000000000000000000000000000006",
  "decimals": 6,
  "balance_raw": "1050000",
  "balance_formatted": 1.05
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/base-mainnet-erc-20-token-balance-lookup-88860933/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402-data-api.sigrunner.workers.dev](https://www.zero.xyz/host/x402-data-api.sigrunner.workers.dev/llms.txt)