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Function Selector Encoder
x402
Function Selector Encoder is a paid API for AI agents from 402.com.tr, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-15).
Computes the 4-byte ABI function selector from a Solidity function signature string (e.g. transfer(address,uint256) → 0xa9059cbb)
Price / call$0.01
Success—
StatusUnknown
How this service works
Computes the 4-byte selector for a function signature (e.g. transfer(address,uint256) → 0xa9059cbb). The inverse of the decoder — useful for agents building or matching calldata.
Output
Returns the 4-byte hexadecimal function selector (e.g. 0xa9059cbb) derived by taking the first 4 bytes of the keccak256 hash of the canonical function signature string. This is the same discriminator prefix prepended to EVM calldata to identify which function is being invoked.
Example use cases
Verify calldata method routing
“I have raw calldata starting with 0xa9059cbb — can you confirm that encodes to the transfer(address,uint256) selector so I know which function is being called?”
Build calldata for contract interaction
“I'm constructing an ERC-20 approve call manually — what's the 4-byte selector for approve(address,uint256) so I can prepend it to my encoded parameters?”
Match selector in transaction decoder
“My transaction decoder found function ID 0x095ea7b3 — can you encode approve(address,uint256) to a selector and confirm they match?”
Technical details
Endpoint
GEThttps://402.com.tr/api/x402/encode-selectorWhen to prefer
Use this endpoint when you need to programmatically compute the EVM calldata selector for a known function signature, especially when building or validating raw calldata, matching an unknown 4-byte prefix to a known function, or checking selector collisions. Prefer this over doing the keccak256 hash manually when working in an agent context that doesn't have direct cryptographic primitives available.
Side effects
- Missing 'signature' query parameter returns an error
- Malformed or non-canonical function signature (e.g. spaces, wrong type names) may produce an unexpected selector or validation error
- Network timeout or service unavailability returns a non-200 response
- Invalid method type other than GET is rejected
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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