# EVM Function Selector & Event Topic Decoder

> EVM Function Selector & Event Topic Decoder is a paid API for AI agents from task-radar-x402.vercel.app, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-31).

Decodes 4-byte function selectors and 32-byte event topics into human-readable text signatures using the Openchain database

## Facts

- Endpoint: GET https://task-radar-x402.vercel.app/api/signature?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-31
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/evm-function-selector-event-topic-decoder-57bc06e1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_HWubCcjfkA6kc8Lf0In7o

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 evm-function-selector-event-topic-decoder-57bc06e1
```

Example prompt: What function does the selector 0xa9059cbb map to, and can you also decode the event topic 0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef?

## When to prefer this

Use this endpoint when you need to reverse-lookup EVM function selectors or event topic hashes into human-readable ABI signatures, especially during transaction analysis, calldata decoding, or smart contract auditing. It supports batch lookup of up to 20 selectors/topics per call, making it efficient for bulk decoding. Prefer this over a full transaction decoder when you only have raw selectors and don't need full transaction context.

## Known failure modes

- Unknown selector or topic not found in Openchain database — returns empty or null result for that entry
- Invalid hex format for selector or topic — returns error
- Exceeding 20 selectors per call — returns validation error
- Payment failure on Base network — 402 response requiring USDC payment

## How this service works

Decode 4-byte function selectors and 32-byte event topics to text signatures (openchain). 0.01 USDC/call on Base.

## Output

Returns the human-readable text signature(s) corresponding to the provided 4-byte function selector(s) or 32-byte event topic(s), such as 'transfer(address,uint256)' or 'Transfer(address,address,uint256)', sourced from the Openchain signature database. Up to 20 selectors/topics can be resolved per call.

## 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": {
     "const": "http"
    },
    "method": {
     "const": "GET"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "selector": {
       "type": "string",
       "description": "Comma-separated 0x 4-byte function selectors and/or 0x 32-byte event topics (max 20)"
      }
     }
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/evm-function-selector-event-topic-decoder-57bc06e1/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from task-radar-x402.vercel.app](https://www.zero.xyz/host/task-radar-x402.vercel.app/llms.txt)