# ERC-20 Allowance Checker on Base

> ERC-20 Allowance Checker on Base is a paid API for AI agents from api.api-agent-ia.ch, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-24).

Returns the ERC-20 token allowance a spender is approved to use from an owner's wallet on Base mainnet, flagging unlimited approvals.

## Facts

- Endpoint: GET https://api.api-agent-ia.ch/allowance?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-24
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/erc-20-allowance-checker-on-base-3f3cf1d8
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ySbAwS032EXdCB3CbImU9

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 erc-20-allowance-checker-on-base-3f3cf1d8
```

Example prompt: Before I do this swap, can you check how much USDC (0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48) my wallet 0xAbCd...1234 has approved the Uniswap router 0x3fC9...5678 to spend on Base?

## When to prefer this

Use this endpoint when you need to check an existing ERC-20 token approval on Base mainnet before initiating a DeFi transaction such as a swap, deposit, or transfer. It is ideal for pre-flight checks in DeFi automation agents to avoid unnecessary on-chain approval transactions. Prefer this over general blockchain explorers when you want a structured, agent-consumable response with formatted allowance and unlimited-approval detection.

## Known failure modes

- Invalid 0x address format for token, owner, or spender returns an error
- Token address is not a valid ERC-20 contract on Base returns an error or zero allowance
- Network issues with Base RPC may cause timeouts
- Querying an address with no approval returns allowance of 0

## How this service works

Is a token approval already granted? Returns the ERC-20 allowance an owner gave a spender on Base, raw and formatted, and flags unlimited approvals ($0.002 per call).

## Output

Returns a JSON object containing the owner address, token address, token symbol, spender address, and the formatted allowance amount the spender is approved to use. Unlimited approvals are flagged with a special indicator.

## 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"
      },
      "token": {
       "type": "string"
      },
      "spender": {
       "type": "string"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "owner": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
  "token": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "reseau": "base",
  "symbol": "USDC",
  "spender": "0x000000000022D473030F116dDEE9F6B43aC78BA3",
  "decimals": 6,
  "illimitee": false,
  "allowance_brut": "0",
  "allowance_formate": "0"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/erc-20-allowance-checker-on-base-3f3cf1d8/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.api-agent-ia.ch](https://www.zero.xyz/host/api.api-agent-ia.ch/llms.txt)