# Base ERC-20 Allowance Checker

> Base ERC-20 Allowance Checker is a paid API for AI agents from ca-tax-api-mainnet.lxtap.workers.dev, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-23).

Returns the ERC-20 token allowance a spender has from an owner on Base, including whether it is effectively unlimited, the owner's current balance, and the spendable amount right now.

## Facts

- Endpoint: GET https://ca-tax-api-mainnet.lxtap.workers.dev/base/allowance?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-23
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/base-erc-20-allowance-checker-c71fbbf3
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Ep1v1FFymDN9eRXX24mFb

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-erc-20-allowance-checker-c71fbbf3
```

Example prompt: Check the ERC-20 allowance on Base for token 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48 — how much is spender 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045 approved to transfer from owner 0xAbCd1234AbCd1234AbCd1234AbCd1234AbCd1234, is the approval unlimited, and how much could they actually move given the owner's current balance?

## When to prefer this

Use this endpoint when you need to inspect ERC-20 token approvals specifically on Base mainnet — particularly when you want to know not just the raw allowance but also whether it is effectively unlimited and how much the spender can actually transfer given the owner's real balance. Prefer this over generic blockchain explorers when you need a structured, machine-readable response suitable for automated DeFi workflows, security audits, or approval management agents.

## Known failure modes

- Invalid or malformed Ethereum address format returns a validation error
- Token address is not a valid ERC-20 contract on Base — returns an error or zero values
- Network or RPC timeout causes a 5xx response
- Owner or spender address not found on-chain returns zero allowance and zero balance
- Missing required query parameters (token, owner, spender) returns a 400 bad request

## How this service works

Pay-per-call data for AI agents, paid in USDC on Base with x402: token risk checks (rug check) on Base, Ethereum, Arbitrum, Optimism, Polygon and Solana, onchain reads (balances, transactions, gas, contracts, NFTs, whale trades, new pools, ENS and Basenames), ECB exchange rates, and Canadian sales tax and business days.

## Output

Returns the raw allowance granted by the owner to the spender, a boolean or flag indicating whether the approval is effectively unlimited (e.g. max uint256), the owner's current token balance, and the effective spendable amount (the lesser of allowance and balance) — all for the specified ERC-20 token on Base mainnet.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "token",
      "owner",
      "spender"
     ],
     "properties": {
      "owner": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "Address that granted the approval"
      },
      "token": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "ERC-20 contract on Base"
      },
      "spender": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "Address allowed to spend"
      }
     },
     "additionalProperties": false
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "raw": "0",
  "chain": "base",
  "owner": "0x698229f40EF287c4B470813e95429f8d764E8054",
  "token": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "symbol": "USDC",
  "spender": "0x000000000022D473030F116dDEE9F6B43aC78BA3",
  "allowance": "0",
  "unlimited": false,
  "ownerBalance": "0",
  "spendableNow": "0"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/base-erc-20-allowance-checker-c71fbbf3/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from ca-tax-api-mainnet.lxtap.workers.dev](https://www.zero.xyz/host/ca-tax-api-mainnet.lxtap.workers.dev/llms.txt)