# Solidity Function Selector Calculator

> Solidity Function Selector Calculator is a paid API for AI agents from twin.unykorn.org, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-01).

Computes the 4-byte ABI function selector from a Solidity function signature string

## Facts

- Endpoint: POST https://twin.unykorn.org/abi-function-selector?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-01
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/solidity-function-selector-calculator-10f9ce55
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_fRAU5jt8_JvFGbwLdyY_A

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 solidity-function-selector-calculator-10f9ce55 -d '<json body>'
```

Example prompt: What's the ABI function selector for the Solidity signature transfer(address,uint256)? I need the 4-byte hex value.

## When to prefer this

Choose this endpoint when you need a quick, paid, on-demand computation of the Solidity ABI function selector from a human-readable function signature, especially in agentic workflows that already use the x402 micropayment protocol. Prefer it when you want a verifiable receipt of the computation and are working within the UnyKorn/Genesis402 ecosystem alongside other blockchain utilities like calldata splitting or EVM chain lookups.

## Known failure modes

- Invalid or malformed Solidity signature string causes an error response
- Missing required 'signature' field in the params object
- Network timeout or service unavailability returns a non-200 response
- Payment failure via x402 protocol prevents computation
- Signature with unsupported or non-standard types may produce unexpected results

## How this service works

Function selector from a Solidity signature — Genesis402 / UnyKorn Operator Network

## Output

Returns a JSON object confirming success, the computed 4-byte ABI function selector hex string derived from the provided Solidity signature, along with a payment receipt including transaction hash, amount in USD, and a unique receipt ID.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "params": {
   "type": "object",
   "properties": {
    "signature": {
     "type": "string"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "type": "abi-function-selector",
  "receipt": {
   "tx_hash": "0x<64hex>",
   "amount_usd": 0.001,
   "receipt_id": "g402-<16hex>"
  },
  "generated_at": "<iso8601>"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/solidity-function-selector-calculator-10f9ce55/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from twin.unykorn.org](https://www.zero.xyz/host/twin.unykorn.org/llms.txt)