# PreFlight Checker – x402 Service Auditor

> PreFlight Checker – x402 Service Auditor is a paid API for AI agents from x402-api-catalog.onrender.com, paid per call via x402, $1/call, status unknown (last checked 2026-09-15).

Audits an x402-enabled API endpoint for the specific failure modes that cause aggregators to mark it as down or its 402 challenge as unreadable, returning concrete diagnoses and fixes.

## Facts

- Endpoint: GET https://x402-api-catalog.onrender.com/api/x402-doctor
- Price: $1/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/preflight-checker-x402-service-auditor-18c96b70
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_aZP3ZmJPPy5HthhSCMDit

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 preflight-checker-x402-service-auditor-18c96b70
```

Example prompt: Can you audit my x402 service at https://my-api.example.com and tell me exactly why it keeps showing as down on Bazaar and x402scan — specifically check the /.well-known/x402 descriptor and whether the live 402 challenge matches what's advertised?

## When to prefer this

Choose this endpoint when you need to understand specifically why an x402-enabled API is being flagged as down or broken by aggregators like agent-tools.cloud, x402scan, or Bazaar. It is purpose-built for the x402 payment protocol and goes beyond simple uptime checks by diagnosing descriptor validity, challenge format, and drift between advertised and live payment terms — making it the right tool for developers debugging x402 integration issues rather than general API health monitoring.

## Known failure modes

- Target URL is unreachable or times out — returns error indicating the service could not be probed
- Target service returns an unexpected response format that prevents analysis
- Missing required 'url' query parameter — returns 400 validation error
- Audited service has no x402 infrastructure at all — returns low score with full diagnostic breakdown
- Rate limit or payment failure for the $1 USDC per call fee

## How this service works

Audits another x402 service for the exact failure modes that cause aggregators (agent-tools.cloud, x402scan, Bazaar) to mark it 'down' or make its 402 challenge unreadable: missing/invalid /.well-known/x402 descriptor, an unpaid request returning 500/404 instead of a clean 402, a malformed or missing payment-required challenge, and drift between the descriptor's advertised terms and the live challenge. Returns a concrete diagnosis and fix for each failing check, not just pass/fail.

## Output

Returns an audit report with a numeric score, an overall verdict, and per-check diagnoses covering: /.well-known/x402 descriptor presence and validity, whether unpaid requests return a clean 402 (not 500/404), whether the payment-required challenge is well-formed, and whether the descriptor's advertised terms match the live challenge — each with a concrete fix recommendation.

## 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": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "url"
     ],
     "properties": {
      "url": {
       "type": "string",
       "description": "base URL of the x402 service to audit"
      },
      "path": {
       "type": "string",
       "description": "a specific paid endpoint path to probe; omit to auto-discover from the service's /.well-known/x402"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "url": {
       "type": "string"
      },
      "score": {
       "type": "number"
      },
      "verdict": {
       "type": "string"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "url": "https://example-service.onrender.com",
  "fixes": [],
  "score": 40,
  "checks": [],
  "verdict": "broken: aggregators will show this as down"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/preflight-checker-x402-service-auditor-18c96b70/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402-api-catalog.onrender.com](https://www.zero.xyz/host/x402-api-catalog.onrender.com/llms.txt)