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BaseBrief x402 – ERC-20 Token Allowance Lookup
x402
BaseBrief x402 – ERC-20 Token Allowance Lookup is a paid API for AI agents from basebrief-x402.savannah-5966.chatgpt.site, paid per call via x402, $0.004/call, status unknown (last checked 2026-09-15).
Returns the current ERC-20 token allowance granted by an owner address to a spender address on Base mainnet, charged at $0.004 USDC per call via x402.
Price / call$0.004
Success—
StatusUnknown
How this service works
Gas, balances, token metadata and allowances for $0.004 per result.
Output
Returns a JSON object with the current allowance amount (in token base units) between the specified owner and spender for the given ERC-20 token on Base mainnet, along with on-chain evidence including chain ID (8453), block number at query time, and a flag indicating this is a point-in-time snapshot. Includes a limitations array noting the data reflects a single RPC query and may change with subsequent blocks.
Example use cases
Pre-swap allowance check for DeFi agent
“Before executing the swap, check whether wallet 0xUserWallet... has already approved enough USDC (0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913) for the Uniswap v3 router 0x2626664c... to spend on Base mainnet.”
Security audit of wallet approvals
“I want to verify the exact token allowance that my wallet 0xMyWallet... has granted to the Aave lending pool contract 0xAavePoo... for the WETH token 0x4200000000000000000000000000000000000006 on Base — can you fetch the current approved amount?”
Automated DeFi bot pre-flight check
“Before my yield farming bot proceeds, check if wallet 0xBotWallet... has approved the vault contract 0xVaultAddr... to spend cbETH token 0x2Ae3F1Ec... on Base mainnet and tell me the approved allowance.”
Technical details
Endpoint
GEThttps://basebrief-x402.savannah-5966.chatgpt.site/api/v1/base/allowanceWhen to prefer
Use this endpoint when you need a quick, cheap, on-chain point-in-time ERC-20 allowance check specifically on Base mainnet (chain 8453) and want a pay-per-call model via x402 without API key management. Prefer this over general blockchain RPC services when you need structured JSON evidence with provenance metadata rather than raw RPC responses, and when operating in an autonomous agent context that supports x402 micropayments.
Side effects
- Invalid Ethereum address format (not matching ^0x[0-9a-fA-F]{40}$) returns 400 validation error
- Token address is not a valid ERC-20 contract on Base mainnet — may return zero or RPC error
- x402 payment failure if USDC balance or payment authorization is insufficient
- Base mainnet RPC node downtime or latency spikes causing delayed or failed responses
- Queried block may become stale between request and use — allowance can change in subsequent blocks
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"evidence": {
"chain": "Base mainnet",
"chainId": 8453,
"blockNumber": "35123456",
"pointInTime": true
},
"limitations": [
"Point-in-time direct Base JSON-RPC evidence."
]
}
}Tags
x402
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