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Base Address Contract Checker
x402
Base Address Contract Checker 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).
Determines whether a Base mainnet address is a smart contract or an externally owned account (EOA), returning a boolean flag and bytecode size.
Price / call$0.002
Success—
StatusUnknown
How this service works
Is a Base address a smart contract or an EOA? Returns is_contract and bytecode size. Use when an agent must decide whether a recipient is a contract before sending funds or approving it.
Output
Returns a JSON object with the queried address, a boolean is_contract field (true if bytecode is present), an integer code_bytes indicating bytecode size, and the chain identifier ('base'). An EOA will have code_bytes of 0 and is_contract of false; a deployed contract will have code_bytes > 0 and is_contract of true.
Example use cases
Pre-transfer contract safety check
“I'm about to send 500 USDC to 0xAbCd1234AbCd1234AbCd1234AbCd1234AbCd1234 on Base — can you first confirm whether that address is a smart contract or just a regular EOA wallet?”
DeFi approval gate for contract recipients
“Before my agent approves a token allowance to 0x7d2768dE32b0b80b7a3454c06BdAc94A69DDc7A9 on Base, check if it's actually a deployed contract so we don't accidentally approve a random wallet.”
Automated recipient classification in payment flow
“I'm building a payment pipeline on Base and need to know if 0x3fC91A3afd70395Cd496C647d5a6CC9D4B2b7FAD is a contract or a plain address — what does the bytecode check say?”
Technical details
Endpoint
GEThttps://x402-data-api.sigrunner.workers.dev/chain/is-contract?utm_source=zero.xyzWhen to prefer
Use this endpoint when an agent needs to make a binary contract-vs-EOA determination on a Base mainnet address before executing a financial operation such as sending funds, approving token allowances, or whitelisting recipients. It is more lightweight than full contract ABI fetching and purpose-built for the Base chain. Prefer it over generic Ethereum explorers when operating within a Base-native agent workflow that already handles x402 micropayments.
Side effects
- Missing or malformed address parameter — no query param provided or not a valid 0x-prefixed 20-byte hex string
- Address not found / zero-address edge cases returning ambiguous results
- Network or RPC errors on Base mainnet causing lookup failure
- Payment failure (x402 USDC payment not fulfilled) resulting in 402 response
- Rate limiting or infrastructure errors returning 5xx responses
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"chain": "base",
"address": "0x4200000000000000000000000000000000000006",
"code_bytes": 2000,
"is_contract": true
}
}Tags
x402
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