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ABI Encode – EVM Contract Function Calldata Encoder
x402
ABI Encode – EVM Contract Function Calldata Encoder is a paid API for AI agents from api.vextorium.com, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-15).
Encodes a Solidity function signature and arguments into ABI-encoded calldata (selector + hex data) ready to sign, broadcast, or simulate on EVM chains.
Price / call$0.003
Success—
StatusUnknown
How this service works
Encode a contract function call (calldata) from its signature and arguments, e.g. transfer(address,uint256) with [to, amount]: selector and hex data ready to sign or simulate.
Output
Returns a JSON object with the hex-encoded calldata string (including 4-byte selector prefix), the isolated 4-byte function selector, the canonical function signature string, and the total byte length of the calldata. For example: {"calldata":"0xa9059cbb0000...","selector":"0xa9059cbb","function":"transfer(address,uint256)","bytes":68}.
Example use cases
Build raw ERC-20 transfer calldata
“Encode the calldata for an ERC-20 transfer call — function is transfer(address,uint256), recipient is 0xAbCd1234AbCd1234AbCd1234AbCd1234AbCd1234, and the amount is 500000000000000000.”
Simulate a DeFi deposit transaction
“I need the ABI-encoded calldata to call deposit(uint256,address) with amount 1000000000 and receiver 0x7e5F4552091A69125d5DfCb7b8C2659029395Bdf so I can simulate the transaction before sending.”
Get function selector for a contract method
“What's the 4-byte function selector and full calldata for calling approve(address,uint256) with spender 0xDEADbeef00000000000000000000000000000001 and value 115792089237316195423570985008687907853269984665640564039457584007913129639935?”
Technical details
Endpoint
POSThttps://api.vextorium.com/v1/abi-encode?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need to programmatically construct raw EVM calldata from a Solidity function signature and typed arguments — especially for transaction simulation, raw signing, or building payloads for multicall contracts. Prefer it over client-side ethers.js/viem encoding when running in a server-less or agent context without a JS runtime, or when you need a lightweight HTTP call to produce deterministic calldata without installing a full Web3 library.
Side effects
- Invalid or malformed function signature returns an error (e.g. missing parentheses or unknown types)
- Argument count mismatch with the function signature causes encoding failure
- Unsupported Solidity types (e.g. tuple/struct variants) may not encode correctly
- Malformed address arguments (wrong length or non-hex) cause encoding errors
- Empty or missing function field returns a validation error
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| function | string | |
| arguments | array |
Output
Schema · Response
{
"type": "json",
"example": {
"bytes": 68,
"calldata": "0xa9059cbb0000000000000000000000007e5f4552091a69125d5dfcb7b8c2659029395bdf00000000000000000000000000000000000000000000000000000000000f4240",
"function": "transfer(address,uint256)",
"selector": "0xa9059cbb"
}
}Tags
x402
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