# Quartermaster ETH/ERC-20 Balance Checker on Base

> Quartermaster ETH/ERC-20 Balance Checker on Base is a paid API for AI agents from quartermaster.surewhynot.app, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).

Returns the ETH or ERC-20 (e.g. USDC) token balance of a given wallet address on the Base blockchain for pre-flight funding checks.

## Facts

- Endpoint: GET https://quartermaster.surewhynot.app/v1/balance
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/quartermaster-eth-erc-20-balance-checker-on-base-4eb3a932
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_BSwScYAmvpgH-JZZrjPL8

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 quartermaster-eth-erc-20-balance-checker-on-base-4eb3a932
```

Example prompt: Before sending the payment, check whether wallet 0xAbC1234567890abcdef1234567890abcdef123456 has enough USDC on Base to cover it — look up its USDC balance for me.

## When to prefer this

Use this endpoint when you need to verify a wallet's on-chain token balance on Base before executing or approving a payment, particularly in x402 payment workflows. Prefer this over generic block explorers when you need a programmatic, agent-callable balance check with minimal latency.

## Known failure modes

- Invalid or malformed EVM address (not matching 0x + 40 hex chars) returns a validation error
- Unknown or invalid ERC-20 contract address returns an error or zero balance
- Network issues reaching Base RPC return a connectivity error
- Rate limiting or payment failure (x402) if the $0.001 USDC fee is not satisfied

## How this service works

Check ETH and USDC (or any ERC-20) balance of an address on Base — pre-flight funding checks for payments and settlement.

## Output

Returns the token balance (as a numeric amount) for the queried EVM address on Base, for either ETH, USDC (default), or any specified ERC-20 contract address.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "address"
     ],
     "properties": {
      "token": {
       "type": "string",
       "default": "usdc",
       "description": "'usdc' or an ERC-20 contract address"
      },
      "address": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "EVM address to check on Base"
      }
     }
    }
   },
   "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/quartermaster-eth-erc-20-balance-checker-on-base-4eb3a932/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from quartermaster.surewhynot.app](https://www.zero.xyz/host/quartermaster.surewhynot.app/llms.txt)