# Quartermaster ERC-20 Allowance Checker

> Quartermaster ERC-20 Allowance Checker 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).

Checks the ERC-20 token spending allowance granted by an owner to a spender on Base, and flags if the approval is unlimited.

## Facts

- Endpoint: GET https://quartermaster.surewhynot.app/v1/base/allowance
- 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-erc-20-allowance-checker-2b6133d1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_TaHZAK73gjg9qzo_8jRs5

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-erc-20-allowance-checker-2b6133d1
```

Example prompt: Can you check how much USDC spending allowance my wallet 0xAbc123... has granted to the Uniswap router at 0xDef456... on Base, and let me know if it's an unlimited approval?

## When to prefer this

Use this endpoint when you need to check the exact ERC-20 token allowance between two Base addresses, especially to detect risky unlimited approvals. Prefer this over generic block explorers when you need a structured, programmatic JSON response with an explicit unlimited-approval flag ready for agent workflows.

## Known failure modes

- Invalid Ethereum address format for owner or spender returns a 400 error
- Unknown or unsupported token symbol returns an error
- RPC or Base node connectivity issues may cause timeout
- Missing required owner or spender query parameters returns a 400 error
- Payment not provided or insufficient USDC results in a 402 response

## How this service works

Check an ERC-20 spending allowance on Base; flags unlimited approvals.

## Output

Returns the current ERC-20 token allowance amount approved by the owner address for the spender address on Base, along with a flag indicating whether the approval is unlimited (max uint256). Includes the token and addresses involved.

## 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": [
      "owner",
      "spender"
     ],
     "properties": {
      "owner": {
       "type": "string"
      },
      "token": {
       "type": "string",
       "default": "usdc"
      },
      "spender": {
       "type": "string"
      }
     }
    }
   },
   "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-erc-20-allowance-checker-2b6133d1/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)