# X402 Challenge Shape Check

> X402 Challenge Shape Check is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-13).

Validates the required top-level fields and structure of a caller-supplied x402 payment challenge object, returning acceptance/rejection status and mismatch reasons.

## Facts

- Endpoint: POST https://api.delx.ai/api/v1/x402/x402-challenge-shape-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-challenge-shape-check-69b0e45a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_wscA5K3DhkA9ypOI1ZV-l

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 x402-challenge-shape-check-69b0e45a -d '<json body>'
```

Example prompt: Before we accept or pay this x402 challenge, can you run a shape check on it to confirm all the required top-level fields are present and the structure is valid — and tell me if anything is missing or mismatched?

## When to prefer this

Use this endpoint when you need a fast, cheap ($0.001 USDC), stateless structural check on an x402 payment challenge before committing to paying or accepting it. Prefer this over manual field inspection when building agent pipelines that need to gate on challenge validity. It processes in memory without data retention, making it suitable for sensitive challenge objects.

## Known failure modes

- Challenge object exceeds 128 properties limit, causing rejection
- Missing required top-level fields result in explicit rejection status with enumerated mismatch reasons
- Malformed JSON in the challenge object may cause a parsing error
- Empty challenge object returns rejection with all required fields listed as missing
- Network or service errors return HTTP 4xx/5xx without a validation result

## How this service works

X402 Challenge Shape Check: X402 Challenge Shape Check checks required top-level fields in a caller-supplied payment challenge from bounded caller-supplied values without an external provider. Call X402 Challenge Shape Check before paying for or accepting an x402 or agent delivery assembled from caller-supplied challenge and result metadata. Returns contract-specific checks, normalized evidence, mismatch reasons, and an explicit acceptance or rejection status for X402 Challenge Shape Check as v…

## Output

Returns a structured result including: an explicit acceptance or rejection status for the challenge, contract-specific field checks, normalized evidence derived from the challenge, and a list of mismatch reasons explaining any structural problems found.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "challenge": {
   "type": "object",
   "description": "Challenge supplied to X402 Challenge Shape Check; used only for this bounded calculation and processed in memory without retention.",
   "maxProperties": 128,
   "additionalProperties": true
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "result": {
   "shape_valid": true,
   "accept_count": 1,
   "missing_fields": []
  },
  "schema": "delx/util-x402-challenge-shape-check/v1",
  "status": "pass",
  "evidence": {
   "retained": false,
   "input_sha256": "62072ab7fce77c19843d604f1566016ce4dbe3ea291d11d208433c905228eeab",
   "external_calls": 0
  },
  "operation": "delivery_contract:x402_challenge_shape_check"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-challenge-shape-check-69b0e45a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.delx.ai](https://www.zero.xyz/host/api.delx.ai/llms.txt)