# Ethereum ERC-20 Allowance Checker

> Ethereum ERC-20 Allowance Checker is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-21).

Returns the ERC-20 token allowance (raw and human-readable) that an owner has granted to a spender on Ethereum mainnet

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/eth-erc20-allowance?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-21
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/ethereum-erc-20-allowance-checker-691e8427
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_lBNsFYn6xyxNNgWJDaOJ0

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 ethereum-erc-20-allowance-checker-691e8427 -d '<json body>'
```

Example prompt: What's the current USDC allowance that 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045 has granted to the Uniswap v3 router 0xE592427A0AEce92De3Edee1F18E0157C05861564 on Ethereum mainnet?

## When to prefer this

Choose this endpoint when you need a read-only, on-chain ERC-20 allowance lookup for Ethereum mainnet and want both raw and decimal-adjusted values in a single call. It's priced at $0.002 USDC per call and has a free sandbox at /v1/sandbox/eth-erc20-allowance for testing. Prefer it over building your own RPC calls when you need a simple, hosted allowance query without managing Ethereum node infrastructure.

## Known failure modes

- Invalid or non-checksummed Ethereum address returns a 400 error
- Token contract address does not implement ERC-20 allowance() function returns an error
- Ethereum node unavailable or rate-limited returns a 503 or timeout
- Decimals not readable — returns raw value only without human-readable amount
- Payment not included or insufficient — returns 402 Payment Required; use sandbox endpoint first

## How this service works

Call when an agent needs ERC-20 allowance(owner, spender) on Ethereum, raw and human when decimals() is readable. Send token, owner, and spender. Read-only. No spend. Send JSON {"token":"0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48","owner":"0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045","spender":"0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48"}. Exact $0.002 USDC on Base. Try unpaid POST /v1/sandbox/eth-erc20-allowance first.

## Output

Returns the allowance amount in two forms: raw (as the integer value from the contract) and human-readable (scaled by the token's decimals() value if readable), representing how many tokens the spender is authorized to transfer on behalf of the owner.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "owner": {
   "type": "string",
   "examples": [
    "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"
   ],
   "description": "Token holder who granted the allowance. Example: 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045. EIP-55 or all one case."
  },
  "token": {
   "type": "string",
   "examples": [
    "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48"
   ],
   "description": "ERC-20 contract on Ethereum mainnet. Example: 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48 (Circle USDC). allowance(owner, spender) is read-only."
  },
  "spender": {
   "type": "string",
   "examples": [
    "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48"
   ],
   "description": "Account allowed to spend the tokens. Example: 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48. EIP-55 or all one case."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/ethereum-erc-20-allowance-checker-691e8427/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agentshelf.syntexa.ch](https://www.zero.xyz/host/agentshelf.syntexa.ch/llms.txt)