# Base ERC20 Allowance Lookup

> Base ERC20 Allowance Lookup is a paid API for AI agents from x402.agentindex.world, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-10).

Reads the ERC20 token allowance on Base mainnet — how many tokens a spender is approved to transfer from an owner's wallet — via an eth_call to the allowance(owner,spender) function.

## Facts

- Endpoint: GET https://x402.agentindex.world/base/allowance?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-10
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/base-erc20-allowance-lookup-3e6fc0fb
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_vSQjCkUa0KwbT9jknjcc4

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-erc20-allowance-lookup-3e6fc0fb
```

Example prompt: Check how much USDC (0xd9aAEc86B65D86f6A7B5B1b0c42FFA531710b6CA) the Uniswap v3 router (0x2626664c2603336E57B271c5C0b26F421741e481) is approved to spend from my wallet 0xAbCd1234...5678 on Base mainnet.

## When to prefer this

Use this endpoint when you specifically need to read ERC20 token allowances on Base mainnet without managing your own RPC node or web3 infrastructure. Ideal for AI agents that need on-chain approval state before executing or recommending DeFi actions on Base. Prefer this over a generic Ethereum allowance checker when the user is operating on Base (Coinbase L2). The pay-per-call x402 model makes it cost-efficient for low-frequency spot checks without subscription overhead.

## Known failure modes

- Invalid or non-checksummed Ethereum address for owner, spender, or token — returns error or unexpected result
- Token address is not a valid ERC20 contract on Base mainnet — eth_call may revert or return empty
- Base RPC node downtime or network congestion causing timeout
- Payment failure (x402) if insufficient USDC balance for the $0.003 fee
- Querying a token that exists on Ethereum mainnet but not on Base — returns zero allowance misleadingly

## How this service works

ERC20 spending allowance an owner has granted a spender on Base mainnet, via allowance(owner,spender).

## Output

Returns the current ERC20 allowance as an integer (or formatted token amount) representing the number of tokens the spender is approved to transfer from the owner's balance for the specified token contract on Base mainnet. A value of zero means no approval exists; a very large value (e.g. max uint256) typically indicates an unlimited approval.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "owner": {
   "type": "string",
   "title": "Owner"
  },
  "token": {
   "type": "string",
   "title": "Token"
  },
  "spender": {
   "type": "string",
   "title": "Spender"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/base-erc20-allowance-lookup-3e6fc0fb/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.agentindex.world](https://www.zero.xyz/host/x402.agentindex.world/llms.txt)