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ERC-20 Allowance Lookup on Base
x402
ERC-20 Allowance Lookup on Base is a paid API for AI agents from x402-data-api.sigrunner.workers.dev, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-20).
Returns the ERC-20 token allowance granted by an owner to a spender on Base, with raw and formatted values plus an unlimited approval flag.
Price / call$0.002
Success—
StatusUnknown
How this service works
ERC-20 allowance(owner, spender) on Base, raw + formatted, flags unlimited approvals.
Output
Returns a JSON object containing the chain (base), owner address, token address, spender address, token decimals, the allowance as a human-readable integer, the raw allowance string (in smallest units), and a boolean is_unlimited flag indicating whether the approval is effectively unlimited (max uint256).
Example use cases
Pre-trade approval check for DeFi agent
“Before executing this swap, check whether wallet 0xAbCd...1234 has approved the Uniswap router 0x4200000000000000000000000000000000000006 to spend USDC (0x833589fCd6eDb6E08f4c7C32D4f71b54bdA02913) on Base, and tell me if the allowance is unlimited.”
Unlimited approval security audit
“Scan wallet 0x5765ae06a52dc7A0BB71c36A11db512c7ea9ed10 — does it have an unlimited USDC approval set for the contract 0x4200000000000000000000000000000000000006 on Base? Flag it if so.”
Allowance sufficiency check before transfer
“I want to send 500 USDC on Base using the contract 0x4200000000000000000000000000000000000006 from owner 0x5765ae06a52dc7A0BB71c36A11db512c7ea9ed10 — check if the current allowance is enough to cover that amount.”
Technical details
Endpoint
GEThttps://x402-data-api.sigrunner.workers.dev/chain/allowance?utm_source=zero.xyzWhen to prefer
Choose this endpoint when an AI agent needs to programmatically check ERC-20 token approvals on Base before executing a trade, transfer, or DeFi interaction — especially when detecting unlimited approvals is important for security gating. Prefer this over general blockchain RPCs when you want a pre-parsed, human-readable allowance with the unlimited flag already computed, without writing custom on-chain call logic.
Side effects
- Invalid or malformed owner/spender/token address returns an error or empty result
- Token address not an ERC-20 contract on Base may return zero allowance or error
- Network/RPC issues on Base may cause timeouts
- Missing required query parameters (owner, token, spender) results in a bad request response
- Payment failure via x402 protocol blocks access to the endpoint
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"chain": "base",
"owner": "0x5765ae06a52dc7A0BB71c36A11db512c7ea9ed10",
"token": "0x833589fCd6eDb6E08f4c7C32D4f71b54bdA02913",
"spender": "0x4200000000000000000000000000000000000006",
"decimals": 6,
"allowance": 0,
"is_unlimited": false,
"allowance_raw": "0"
}
}Tags
x402
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