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Base Onchain Tools – ERC-20 Allowance Check
x402
Base Onchain Tools – ERC-20 Allowance Check is a paid API for AI agents from base-onchain-tools.dolerite.workers.dev, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-10).
Checks whether a given spender address has an active ERC-20 token approval from a token holder on Base mainnet, returning the verdict and approval details.
Price / call$0.001
Success—
StatusUnknown
How this service works
Eleven read-only endpoints answering questions about Base mainnet that are tedious to assemble from raw RPC: what an unverified contract is actually able to do, whether a token transfer will revert and for what reason, what an arbitrary token is worth, and whether an address is safe to pay. Priced $0.001-$0.04 per call in USDC over x402. No account, no API key, no signup, no minimum, no rate limit to negotiate — the payTo address in the 402 response is the whole integration. Failed calls are not billed. The payment middleware cancels settlement on any 4xx or 5xx, so a malformed parameter or an upstream outage costs nothing. Answers are read live from Base mainnet at request time, with failover across five independent RPC providers. A batch that comes back incomplete is treated as a failure rather than returned with the missing entries as zeros, because a confident wrong answer costs a caller more than an error does. Scope is deliberately narrow: Base mainnet only, reads only, no keys held, nothing stored between requests.
Output
Returns a JSON object with a verdict field (e.g. 'no-approval', 'approved', 'unlimited'), the token_symbol, and an unlimited_approval boolean indicating whether the spender has been granted an unlimited allowance.
Example use cases
Pre-swap approval gate for DeFi agent
“Before I swap on Aerodrome, check if the router at 0x6330...abcd is allowed to spend my USDC from 0x1234...5678 on Base — I need to know if I have to approve first.”
Security audit of unlimited approvals
“Is there an unlimited approval on my wallet 0xDEAD...BEEF for the old Compound contract at 0xABCD...1234 to spend my USDC on Base? I want to know if I need to revoke it.”
DeFi onboarding flow validation
“My app needs to confirm that the lending protocol at 0x9999...aaaa can spend USDC on behalf of the user at 0x1111...bbbb on Base before we proceed with the deposit — can you check that allowance?”
Technical details
Endpoint
GEThttps://base-onchain-tools.dolerite.workers.dev/v1/base/allowance?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need a quick, cheap, read-only check of ERC-20 allowances on Base mainnet without setting up a wallet, API key, or RPC infrastructure. Ideal for pre-flight checks before DeFi transactions, security audits of token approvals, or any agent flow that must gate on whether a spender is authorized. Prefer this over raw RPC calls because it abstracts multi-provider failover, returns a human-readable verdict, and charges nothing on failure.
Side effects
- Invalid or non-checksummed Ethereum address returns 4xx with no charge
- Token address not found or not an ERC-20 contract returns an error
- Upstream RPC outage across all five providers causes a 5xx with no charge
- Missing required owner or spender query parameters returns 4xx
- Network timeout on Base mainnet read returns 5xx with no charge
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"verdict": "no-approval",
"token_symbol": "USDC",
"unlimited_approval": false
}
}Tags
x402
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