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ERC-20 Token Allowance Checker
x402
ERC-20 Token Allowance Checker is a paid API for AI agents from x402-gateway-production-1f21.up.railway.app, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-10).
Looks up the current ERC-20 token allowance granted by an owner address to a spender address on a given contract and network.
Price / call$0.001
Success—
StatusUnknown
How this service works
Machine-payable x402 utilities for hashing, Base64, UUID generation, unit and timezone conversion, realtime crypto market data, webpage/document extraction, URL-to-Markdown, metadata, RAG ingestion and deterministic website change detection.
Output
Returns a JSON object indicating the current ERC-20 allowance (as a token amount) that the owner address has approved for the spender address on the specified contract and network, along with a status field confirming the query succeeded.
Example use cases
Pre-swap allowance audit
“Before I execute this swap, check whether my wallet 0xOwnerAddress has already approved the Uniswap router 0xSpenderAddress to spend my USDC at contract 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48 on Ethereum — I need to know the current allowance.”
DeFi protocol approval check
“I'm about to deposit into a yield vault on Base. Can you look up the current token allowance that 0xMyWallet has given to the vault contract 0xVaultAddress for the USDC token at 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 on base?”
Security audit of wallet approvals
“I want to audit my wallet's token approvals — check how much allowance 0xMyWallet has granted to 0xSuspiciousContract on the DAI contract 0x6B175474E89094C44Da98b954EedeAC495271d0F on Ethereum so I know if I should revoke it.”
Technical details
Endpoint
GEThttps://x402-gateway-production-1f21.up.railway.app/erc20-allowance?utm_source=zero.xyzWhen to prefer
Use this endpoint when an AI agent needs to programmatically check ERC-20 token approval state on Base or Ethereum before executing a DeFi transaction, auditing wallet permissions, or determining if an additional approve() call is needed. It is preferable when you need a quick, pay-per-use lookup without managing your own blockchain RPC infrastructure or maintaining a Web3 connection.
Side effects
- Invalid Ethereum address format (not matching 0x + 40 hex chars) returns a 400 error
- Unsupported network value (not 'base' or 'ethereum') returns a validation error
- Contract address is not a valid ERC-20 contract — may return zero or error
- Payment not provided or insufficient USDC — returns HTTP 402 requiring x402 micropayment
- RPC or network timeout causes query failure
- Zero allowance returned when no approval has been set (valid response, not an error)
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"status": "ready"
}
}Tags
x402
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