Function selector / event topic API

Compute the 4-byte function selector or 32-byte event topic hash from a human-readable signature. Answers 'selector for transfer(address,uint256)', 'event topic hash', 'what's the 4byte for this function'.

Price$0.01per request

MethodPOST

Route/v1/evm/function-selector

StatusLive

MIME typeapplication/json

Rate limit120/minute

CacheNo cache

evmselector4byteeventtopicabikeccak

API URLhttps://x402.hexl.dev/v1/evm/function-selector

Integration docs

Example request

{
  "signature": "transfer(address,uint256)",
  "type": "function"
}

Example response

{
  "signature": "transfer(address,uint256)",
  "type": "function",
  "selector": "0xa9059cbb"
}

Input schema

{
  "type": "object",
  "required": [
    "signature"
  ],
  "properties": {
    "signature": {
      "type": "string",
      "examples": [
        "transfer(address,uint256)"
      ]
    },
    "type": {
      "type": "string",
      "enum": [
        "function",
        "event"
      ],
      "default": "function"
    }
  }
}

Output schema

{
  "type": "object",
  "required": [
    "signature",
    "type",
    "selector"
  ],
  "properties": {
    "signature": {
      "type": "string"
    },
    "type": {
      "type": "string"
    },
    "selector": {
      "type": "string"
    }
  }
}