# propeller.rocks Function Selector / Event Topic0 Computer

> propeller.rocks Function Selector / Event Topic0 Computer is a paid API for AI agents from propeller.rocks, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Computes the 4-byte function selector or 32-byte event topic0 hash from an ABI function or event signature

## Facts

- Endpoint: GET https://propeller.rocks/selector
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/propeller-rocks-function-selector-event-topic0-computer-29c14d5e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_pb5_RAieDXe93QCWKGfIL

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 propeller-rocks-function-selector-event-topic0-computer-29c14d5e
```

Example prompt: What's the 4-byte function selector for the Solidity signature transfer(address,uint256)?

## When to prefer this

Use this endpoint when you need to derive the canonical 4-byte selector or event topic0 from a human-readable Solidity function or event signature, without running a full ABI encoder or local keccak256 library. Ideal for EVM tooling workflows where you need to identify or filter transactions and logs by selector.

## Known failure modes

- Invalid or malformed signature string returns an error
- Missing signature input returns a validation error
- Network or payment failure results in no response
- Ambiguous signature format may produce unexpected results

## How this service works

Compute the 4-byte function selector or event topic0 from a signature

## Output

Returns the 4-byte function selector (for function signatures) or 32-byte topic0 hash (for event signatures) derived from the keccak256 hash of the input signature string, as a hex-encoded value.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/propeller-rocks-function-selector-event-topic0-computer-29c14d5e/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from propeller.rocks](https://www.zero.xyz/host/propeller.rocks/llms.txt)