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Ethereum Calldata Decoder & Function Selector Calculator
x402
Ethereum Calldata Decoder & Function Selector Calculator is a paid API for AI agents from api.24klabs.ai, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-13).
Computes the keccak256 hash and 4-byte function selector of a Solidity signature string, and optionally ABI-decodes raw hex calldata given an ordered list of static Solidity types.
Price / call$0.002
Success—
StatusUnknown
How this service works
Compute the keccak256 hash and 4-byte function selector of a signature string, and optionally ABI-decode raw hex calldata given an ordered list of static Solidity types.
Output
Returns the keccak256 hash of the input signature, the 4-byte function selector (first 4 bytes of the hash), and — if raw hex calldata and ABI types are provided — an ordered list of decoded parameter values matching the supplied Solidity types.
Example use cases
Decode live transaction calldata
“I've got raw calldata from an Ethereum transaction — '0xa9059cbb000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045000000000000000000000000000000000000000000000000016345785d8a0000' — can you decode it using ABI types ['address','uint256'] and tell me the recipient address and token amount?”
Look up ERC-20 function selector
“What's the 4-byte function selector and full keccak256 hash for the Solidity signature 'approve(address,uint256)'? I need it to verify a contract interaction.”
Debug unknown contract call
“I'm seeing an Ethereum transaction with calldata starting with an unknown selector. Can you compute the function selector for 'swapExactTokensForTokens(uint256,uint256,address[],address,uint256)' so I can check if it matches?”
Technical details
Endpoint
POSThttps://api.24klabs.ai/api/v1/eth-calldata-decodeWhen to prefer
Choose this endpoint when you need to programmatically compute Ethereum function selectors or keccak256 hashes from Solidity signatures without running a local Ethereum toolchain, or when you need to decode raw ABI-encoded calldata from a transaction and know the parameter types. Ideal for smart contract debugging, transaction analysis, and building blockchain developer tooling in an agent workflow.
Side effects
- Invalid or malformed Solidity signature string returns an error
- Hex calldata length mismatch with provided ABI types causes a decode failure
- Unsupported or complex Solidity types (e.g. dynamic arrays, tuples) may not be decodable
- Malformed hex string (missing 0x prefix, odd length) returns a parse error
- Mismatch between number of ABI type entries and encoded calldata parameters causes incorrect or failed decode
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| signature | string |
Output
Schema · Response
{
"type": "json",
"example": {
"selector": "0xa9059cbb"
}
}Tags
x402
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