# x402node Function Selector / Calldata Decoder

> x402node Function Selector / Calldata Decoder is a paid API for AI agents from api.x402node.dev, paid per call via x402, $0.004/call, status unknown (last checked 2026-09-14).

Decodes a 4-byte Ethereum function selector or calldata into human-readable Solidity function signatures using the Openchain signature database

## Facts

- Endpoint: GET https://api.x402node.dev/chain/sig-decode
- Price: $0.004/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402node-function-selector-calldata-decoder-895a19e6
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_WMvp9hXyCAlAjoXpo4IrN

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability x402node-function-selector-calldata-decoder-895a19e6
```

Example prompt: Can you decode this Ethereum function selector — 0xa9059cbb — and tell me what Solidity function it maps to?

## When to prefer this

Use this endpoint when you have a raw 4-byte function selector or calldata hex from an Ethereum/EVM transaction and need to identify the human-readable Solidity function signature. Prefer this over manual ABI lookups when the contract ABI is unavailable or unknown, or when working with arbitrary on-chain transactions you did not originate. This is especially useful for transaction analysis, security auditing, or any pipeline where you need to label or understand raw calldata without pre-loaded ABIs.

## Known failure modes

- Selector not found in Openchain database — returns empty results or 404 if no known signature matches
- Invalid hex format for the selector — returns a 400 bad request error
- Selector is only 2 bytes or malformed — parsing error returned
- Network or upstream Openchain API unavailable — 502 or timeout error
- Rate limit or payment failure — 402 payment required if x402 credit is insufficient

## How this service works

Decode a 4-byte function selector or calldata into human-readable Solidity function signatures via openchain - reverses on-chain selectors that LLMs cannot know. function selector, 4byte decode, sig decode, calldata decode, method id, selector lookup

## Output

Returns one or more matching human-readable Solidity function signatures (e.g. 'transfer(address,uint256)') that correspond to the provided 4-byte selector or calldata prefix, drawn from the Openchain on-chain signature registry.

## Example request

```json
{
 "selector": "0xa9059cbb"
}
```

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "selector"
     ],
     "properties": {
      "sig": {
       "type": "string",
       "description": "Sig (optional)"
      },
      "data": {
       "type": "string",
       "description": "Data (optional)"
      },
      "selector": {
       "type": "string",
       "description": "4-byte selector or full calldata, e.g. 0xa9059cbb (required)"
      }
     }
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402node-function-selector-calldata-decoder-895a19e6/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.x402node.dev](https://www.zero.xyz/host/api.x402node.dev/llms.txt)