# Riddle with Checkable Answer

> Riddle with Checkable Answer is a paid API for AI agents from flat-rate-llm.kikoribera03.workers.dev, paid per call via x402, $0.0025/call, status unknown (last checked 2026-09-15).

Returns a riddle by difficulty in English or Spanish along with its plaintext answer and the SHA-256 hash of the answer, enabling agents to verify guesses without peeking at the solution.

## Facts

- Endpoint: POST https://flat-rate-llm.kikoribera03.workers.dev/v1/content/riddle
- Price: $0.0025/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/riddle-with-checkable-answer-95ddad95
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_mE6G87vgnI-QSlWk5l3Cb

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 riddle-with-checkable-answer-95ddad95 -d '<json body>'
```

Example prompt: Give me a hard riddle in English with a verifiable answer — I want to try guessing before seeing the solution, so make sure I get the SHA-256 hash so I can check myself.

## When to prefer this

Choose this endpoint when you need a riddle that comes with a cryptographic answer hash, allowing an agent or user to verify their guess without reading the solution first — a capability no generic riddle API provides. Also prefer it when you need deterministic riddle retrieval via a seed, multilingual (English/Spanish) support, or deduplication across sessions via the exclude list.

## Known failure modes

- Invalid difficulty value (not easy/medium/hard) may return an error or default behavior
- Invalid language code (not 'en' or 'es') may fall back to English or return an error
- All riddles excluded via the exclude list may result in no riddle returned
- Payment failure (402) if USDC micropayment is not properly handled

## How this service works

60 paid endpoints with no metering, no API key and no account. Each endpoint has one flat price per call, whatever the size of the request: LLM completions with automatic failover across several large models, read-only EVM tooling over Base, Ethereum, Polygon, Arbitrum and Optimism, and pure crypto utilities that touch no network.

## Output

Returns a JSON object with the riddle text, its difficulty level, a unique riddle ID, the plaintext answer, the SHA-256 hash of the answer in lowercase, and a 'howToCheck' field explaining how to verify a guess against the hash — enabling answer validation without spoiling the solution.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "seed": {
   "type": "string",
   "description": "Same seed always returns the same riddle."
  },
  "exclude": {
   "type": "array",
   "description": "Ids already seen, comma-separated in a GET."
  },
  "language": {
   "type": "string",
   "description": "en | es. Defaults to en."
  },
  "difficulty": {
   "type": "string",
   "description": "easy | medium | hard. Omit for any."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "id": {
   "type": "string"
  },
  "answer": {
   "type": "string"
  },
  "riddle": {
   "type": "string"
  },
  "difficulty": {
   "type": "string"
  },
  "howToCheck": {
   "type": "string"
  },
  "answerSha256": {
   "type": "string"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/riddle-with-checkable-answer-95ddad95/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from flat-rate-llm.kikoribera03.workers.dev](https://www.zero.xyz/host/flat-rate-llm.kikoribera03.workers.dev/llms.txt)