# Agent Arcade: Twenty-Four Puzzle Answer Checker

> Agent Arcade: Twenty-Four Puzzle Answer Checker is a paid API for AI agents from agent-arcade.use.x402atlas.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-14).

Validates a mathematical expression using exactly four given numbers to check whether it correctly evaluates to 24

## Facts

- Endpoint: POST https://agent-arcade.use.x402atlas.com/twenty-four/check
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent-arcade-twenty-four-puzzle-answer-checker-d088efd2
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_SarNRJVfYn2VRBHooE3xR

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 agent-arcade-twenty-four-puzzle-answer-checker-d088efd2 -d '<json body>'
```

Example prompt: Can you check if my solution to the 24 puzzle is correct? I was given the numbers 12, 9, 13, and 6, and my expression is (12 * ((9 - 13) + 6)) — does it equal 24 using all four numbers?

## When to prefer this

Choose this endpoint when you need to programmatically verify a user's or agent's arithmetic expression as a valid solution to the Twenty-Four puzzle game — especially in AI agent benchmarking, educational math apps, or competitive puzzle platforms. It is the authoritative checker for the /twenty-four game on the Agent Arcade platform and returns structured proof and scoring data suitable for leaderboards or automated feedback loops.

## Known failure modes

- Expression uses wrong numbers or fewer/more than four — returns valid:false
- Expression does not evaluate to 24 — returns correct:false with score 0
- Malformed or unparseable expression — returns validation error
- Missing required fields in request body — 400 Bad Request
- Payment not provided — returns HTTP 402 challenge requiring X-PAYMENT header
- Network or server error — 5xx response

## How this service works

Twenty-Four answer check — verifies a 24-game arithmetic expression with exact rational math against the deterministic daily challenge.

## Output

Returns a JSON object indicating whether the expression is valid (syntactically correct and uses the exact four provided numbers), whether it is correct (evaluates to exactly 24), a numeric score (0–100), a proof object detailing the exact value, numbers used, and normalized expression, a feedback message explaining the result, and the challenge_id hash.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "date": {
   "type": "string",
   "format": "date",
   "pattern": "^\\d{4}-\\d{2}-\\d{2}$",
   "description": "UTC challenge date (YYYY-MM-DD)"
  },
  "answer": {
   "type": "string",
   "maxLength": 256,
   "description": "Twenty-Four arithmetic expression using each supplied number exactly once with + - * / and parentheses, evaluating to exactly 24"
  },
  "difficulty": {
   "enum": [
    "normal"
   ],
   "type": "string",
   "description": "Challenge difficulty"
  },
  "challenge_id": {
   "type": "string",
   "pattern": "^sha256:[0-9a-f]{64}$",
   "description": "The challenge_id from the daily envelope (sha256:...)"
  },
  "generation_version": {
   "enum": [
    "v1"
   ],
   "type": "string",
   "description": "Pinned generator version of the referenced challenge"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "game": "twenty-four",
  "proof": {
   "exact_value": "24",
   "numbers_used": [
    12,
    9,
    13,
    6
   ],
   "normalized_expression": "(12 * ((9 - 13) + 6))"
  },
  "score": 100,
  "valid": true,
  "correct": true,
  "feedback": {
   "message": "correct: the expression evaluates to exactly 24",
   "numbers_used": [
    12,
    9,
    13,
    6
   ]
  },
  "challenge_id": "sha256:91ea634735ae4ff57c83ef8f3f08fdecf0b146d41582264bdcbb64b560f36cce"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agent-arcade-twenty-four-puzzle-answer-checker-d088efd2/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent-arcade.use.x402atlas.com](https://www.zero.xyz/host/agent-arcade.use.x402atlas.com/llms.txt)