# BaseBrief x402 – ERC-20 Token Allowance Lookup

> BaseBrief x402 – ERC-20 Token Allowance Lookup is a paid API for AI agents from basebrief-x402.savannah-5966.chatgpt.site, paid per call via x402, $0.004/call, status unknown (last checked 2026-09-15).

Returns the current ERC-20 token allowance granted by an owner address to a spender address on Base mainnet, charged at $0.004 USDC per call via x402.

## Facts

- Endpoint: GET https://basebrief-x402.savannah-5966.chatgpt.site/api/v1/base/allowance
- Price: $0.004/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/basebrief-x402-erc-20-token-allowance-lookup-db79512b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Hh9UA8inFRvVt7zw1tLyJ

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 basebrief-x402-erc-20-token-allowance-lookup-db79512b
```

Example prompt: Check how much USDC (token 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913) the owner wallet 0xAbCd1234... has approved for the Uniswap router 0x2626664c... to spend on Base mainnet.

## When to prefer this

Use this endpoint when you need a quick, cheap, on-chain point-in-time ERC-20 allowance check specifically on Base mainnet (chain 8453) and want a pay-per-call model via x402 without API key management. Prefer this over general blockchain RPC services when you need structured JSON evidence with provenance metadata rather than raw RPC responses, and when operating in an autonomous agent context that supports x402 micropayments.

## Known failure modes

- Invalid Ethereum address format (not matching ^0x[0-9a-fA-F]{40}$) returns 400 validation error
- Token address is not a valid ERC-20 contract on Base mainnet — may return zero or RPC error
- x402 payment failure if USDC balance or payment authorization is insufficient
- Base mainnet RPC node downtime or latency spikes causing delayed or failed responses
- Queried block may become stale between request and use — allowance can change in subsequent blocks

## How this service works

Gas, balances, token metadata and allowances for $0.004 per result.

## Output

Returns a JSON object with the current allowance amount (in token base units) between the specified owner and spender for the given ERC-20 token on Base mainnet, along with on-chain evidence including chain ID (8453), block number at query time, and a flag indicating this is a point-in-time snapshot. Includes a limitations array noting the data reflects a single RPC query and may change with subsequent blocks.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "token",
      "owner",
      "spender"
     ],
     "properties": {
      "owner": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "Base mainnet owner address."
      },
      "token": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "Base mainnet token address."
      },
      "spender": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "Base mainnet spender address."
      }
     },
     "additionalProperties": false
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "required": [
      "evidence",
      "limitations"
     ],
     "properties": {
      "evidence": {
       "type": "object",
       "additionalProperties": true
      },
      "limitations": {
       "type": "array",
       "items": {
        "type": "string"
       }
      }
     },
     "additionalProperties": true
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "evidence": {
   "chain": "Base mainnet",
   "chainId": 8453,
   "blockNumber": "35123456",
   "pointInTime": true
  },
  "limitations": [
   "Point-in-time direct Base JSON-RPC evidence."
  ]
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/basebrief-x402-erc-20-token-allowance-lookup-db79512b/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from basebrief-x402.savannah-5966.chatgpt.site](https://www.zero.xyz/host/basebrief-x402.savannah-5966.chatgpt.site/llms.txt)