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Web3 Tools – Solidity Function Selector & Event Topic0 Computer
x402
Web3 Tools – Solidity Function Selector & Event Topic0 Computer is a paid API for AI agents from web3-tools.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-21).
Computes the 4-byte function selector and 32-byte event topic0 from a canonical Solidity signature string
Price / call$0.02
Success—
StatusUnknown
How this service works
Compute the 4-byte function selector and event topic0 from a Solidity signature such as transfer(address,uint256).
Output
Returns a JSON object containing the 4-byte hex function selector, the 32-byte event topic0 hash, the canonical signature string, parameter list, a human-readable name, source attribution, optional warnings or reasons, and a disclaimer field.
Example use cases
Decode unknown EVM calldata
“I'm seeing transactions calling an unknown contract and the first 4 bytes are 0xa9059cbb — can you tell me which Solidity function that selector corresponds to by computing it from transfer(address,uint256)?”
Build smart contract event filter
“I need to set up a log filter for the Transfer(address,address,uint256) event — what is its topic0 hash so I can use it in an eth_getLogs call?”
Verify ABI selector before deployment
“Before I deploy my contract, can you confirm that the function selector for approve(address,uint256) is 0x095ea7b3 so I know my ABI encoding is correct?”
Technical details
Endpoint
GEThttps://web3-tools.x402tookit.com/function-selector?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need to deterministically compute the EVM function selector or event topic0 from a raw Solidity ABI signature string — particularly useful for calldata decoding, event log filtering, ABI verification, or smart contract interaction where you need to confirm the 4-byte method ID without running a local Ethereum toolchain.
Side effects
- Missing or malformed 'signature' query parameter returns an error
- Non-canonical signature with spaces or parameter names may produce incorrect or rejected results
- Unsupported or invalid Solidity types in the signature may cause computation failure
- Network or payment (x402) errors may prevent the call from completing
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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