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ERC-20 Allowance Checker (Base / Optimism / Mainnet)
x402
ERC-20 Allowance Checker (Base / Optimism / Mainnet) is a paid API for AI agents from x402-audit.tatschluizguilherme.workers.dev, paid per call via x402, $0.1/call, status unknown (last checked 2026-09-14).
Returns the on-chain ERC-20 allowance (how much a spender is permitted to transfer from an owner wallet) on Base, Optimism, or Ethereum Mainnet, including formatted amount, decimals, symbol, and block number.
Price / call$0.1
Success—
StatusUnknown
How this service works
Pay-per-call on-chain API for AI agents and developers: wallet audits, token safety audits (honeypot detection), live gas prices, token prices, transaction receipts, balances, ENS resolution, block data, ERC-20 allowances, transaction simulation, swap quotes and multicall batches — all computed on-chain via public RPCs (no external market API). Pay per request in USDC on Base via the x402 exact scheme (EIP-3009 transferWithAuthorization). No API key, no signup, no subscription.
Output
Returns a JSON object containing: the token contract address, owner address, spender address, the allowance in wei (raw), the formatted allowance (human-readable decimal), the token symbol, token decimals, and the block number at which the query was made — all retrieved directly from on-chain RPC without relying on any block explorer API.
Example use cases
Pre-swap approval check on Base
“Before I swap, check if the 1inch router at 0x1111111254EEB25477B68fb85Ed929f73A960582 is approved to spend my USDC (0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913) on Base — my wallet is 0xAbCd1234...5678. How much is it allowed to move?”
DeFi security audit of wallet allowances
“I want to audit my wallet 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045 — check if the Aave v3 pool contract 0x794a61358D6845594F94dc1DB02A252b5b4814aD is approved to spend any WETH (0x4200000000000000000000000000000000000006) on Optimism and tell me the exact allowance.”
Smart contract integration verification
“I'm integrating a new vault contract at 0xVaultAddress on Ethereum Mainnet — can you check whether our token 0xTokenAddress has approved the vault to spend from the deployer wallet 0xDeployerAddress, and tell me the formatted allowance and token decimals?”
Technical details
Endpoint
GEThttps://x402-audit.tatschluizguilherme.workers.dev/allowanceWhen to prefer
Prefer this endpoint when you need a trustless, explorer-independent on-chain allowance check across Base, Optimism, or Ethereum Mainnet. Ideal for pre-transaction approval validation in DeFi workflows, security audits, or any agent pipeline that cannot rely on third-party explorer APIs. Use over block-explorer scraping when you need structured, machine-readable output with wei and formatted values in one call.
Side effects
- Invalid or non-contract token address returns an error or zero allowance
- Unsupported network returns a validation error
- Malformed Ethereum address (wrong checksum or length) causes a request rejection
- Token contract that doesn't implement the ERC-20 allowance function may cause an RPC revert
- Network congestion or RPC timeout may cause a delayed or failed response
Output
Schema · Response
{
"type": "json",
"example": {
"owner": "0x8e8d53a67b59e6f2a28e0d6d52012a2b0e3e1886",
"token": "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913",
"symbol": "USDC",
"network": "base",
"spender": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
"decimals": 6,
"blockNumber": 24400123,
"tokenExists": true,
"allowanceWei": "0",
"allowanceFormatted": "0"
}
}Tags
x402
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