EVM Calldata & Return Data Decoder

x402

EVM Calldata & Return Data Decoder is a paid API for AI agents from api.vextorium.com, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-16).

Decodes EVM transaction input (calldata) into a human-readable function signature and arguments, or decodes return data given output types, using 4byte.directory as fallback for unknown selectors.

Price / call$0.003

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StatusUnknown

How this service works

Decode EVM calldata (transaction input) with the function signature or, if omitted, by looking up the selector on 4byte; or decode return data with its output types (e.g. uint256,address).

Output

Returns the decoded function name (e.g. 'transfer(address,uint256)'), the 4-byte selector (e.g. '0xa9059cbb'), a list of decoded argument values as strings, and the source of the signature (e.g. '4byte.directory' or 'provided').

Example use cases

Decode an unknown transaction input

“I have this raw transaction input from Etherscan: 0xa9059cbb000000000000000000000000abc...0001. Can you decode it for me without knowing the ABI — use 4byte to look up the selector?”

Parse calldata with known function signature

“Decode this calldata using the signature transfer(address,uint256): 0xa9059cbb0000000000000000000000007E5F4552091A69125d5DfCb7b8C2659029395Bdf00000000000000000000000000000000000000000000000000000000000f4240”

Decode smart contract return data

“I called a contract and got back this hex return value: 0x0000000000000000000000000000000000000000000000000de0b6b3a7640000 — decode it as a uint256 so I can see the actual number.”

Technical details

Endpoint

POSThttps://api.vextorium.com/abi-decodificar-pago?utm_source=zero.xyz

When to prefer

Use this endpoint when you need to decode EVM transaction input (calldata) or return data into human-readable arguments without running a full node or maintaining a local ABI database. Especially useful when the function signature is unknown and 4byte.directory lookup is needed. Prefer over manual ABI decoding or ethers.js when operating in a serverless or agent context that calls external APIs.

Side effects

Unknown selector not found on 4byte.directory — returns null signature
Malformed calldata hex causes decoding failure
Wrong function signature provided causes ABI mismatch error
Output types mismatch actual return data length
Missing required 'datos' field returns validation error

Input

Schema · Request body

Field	Type	Description
datos	string
funcion	string
tipos_salida	string

Output

Schema · Response

{
  "type": "json",
  "example": {
    "funcion": "transfer(address,uint256)",
    "selector": "0xa9059cbb",
    "argumentos": [
      "0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf",
      "1000000"
    ],
    "fuente_firma": "4byte.directory"
  }
}

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