# apiacre.com x402 Preflight Checker

> apiacre.com x402 Preflight Checker is a paid API for AI agents from apiacre.com, paid per call via x402, $0.05/call, status unknown (last checked 2026-09-15).

Probes a public API endpoint to assess its x402 payment protocol compliance, returning a grade, protocol evidence, and remediation steps — without paying.

## Facts

- Endpoint: POST https://apiacre.com/v1/developer/x402-preflight
- Price: $0.05/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/apiacre-com-x402-preflight-checker-bc7fa9d9
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_6Ei4g44oprAxvjElODgFO

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 apiacre-com-x402-preflight-checker-bc7fa9d9 -d '<json body>'
```

Example prompt: Run an x402 preflight check on my endpoint at https://api.myproject.com/premium-data and tell me if it passes v2 compliance, what evidence you found, and what I need to fix.

## When to prefer this

Use this endpoint when you need to validate that a public API correctly implements the x402 payment protocol — especially before launching a paid API, integrating a third-party x402 service, or debugging why an x402 payment wall isn't working. It is the only known dedicated x402 compliance grading tool and provides both evidence and remediation, making it superior to manual header inspection.

## Known failure modes

- Target endpoint is unreachable or times out — returns an error with no grade
- Endpoint requires authentication before returning x402 responses — may produce misleading results
- Non-public or firewalled endpoints cannot be probed
- Malformed URL input returns a validation error
- Target server returns unexpected response format that cannot be evaluated

## How this service works

Probe a public endpoint without paying, grade its x402 v2 challenge, check exact-host x402-list presence and traction, and optionally rank licensed market matches with buyer-concentration caveats.

## Output

Returns an x402 v2 compliance grade (e.g. pass/fail/partial), protocol evidence observed from the endpoint's response (headers, status codes, payment details), and actionable remediation steps describing what needs to be added or corrected to achieve full compliance.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string"
  },
  "body": {
   "anyOf": [
    {
     "type": "object"
    },
    {
     "type": "null"
    }
   ]
  },
  "method": {
   "enum": [
    "GET",
    "POST"
   ],
   "type": "string"
  },
  "market_limit": {
   "type": "integer"
  },
  "market_query": {
   "anyOf": [
    {
     "type": "string"
    },
    {
     "type": "null"
    }
   ]
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "data": {
   "url": "https://apiacre.com/v1/developer/openapi-audit",
   "grade": "A",
   "score": 100,
   "checks": [
    {
     "id": "http_402",
     "passed": true,
     "message": "Return HTTP 402 before payment.",
     "severity": "high"
    }
   ],
   "method": "POST",
   "payment": {
    "scheme": "exact",
    "network": "eip155:8453",
    "version": 2,
    "acceptsCount": 1
   },
   "finalUrl": "https://apiacre.com/v1/developer/openapi-audit",
   "checkedAt": "2026-08-09T00:00:00+00:00",
   "compliant": true,
   "elapsedMs": 128,
   "statusCode": 402,
   "limitations": "One unpaid target request only; no payment is signed and ...",
   "remediation": [],
   "gradeVersion": "apiacre-x402-preflight/1",
   "directoryEvidence": {
    "market": {
     "query": "audit",
     "status": "ok",
     "returned": 1,
     "totalMatches": 31
    },
    "source": {
     "url": "https://x402-list.com",
     "name": "x402 List",
     "apiUrl": "https://x402-list.com/api/v1/services",
     "documentationUrl": "https://x402-list.com/api"
    },
    "target": {
     "status": "matched",
     "hostname": "apiacre.com",
     "matchCount": 1,
     "matchMethod": "exact_host"
    },
    "version": "apiacre-x402-directory-evidence/1"
   }
  },
  "meta": {
   "cached": false,
   "sources": [],
   "warnings": [],
   "duration_ms": 42,
   "next_actions": []
  },
  "service": "developer.x402-preflight",
  "version": "1",
  "request_id": "018f1f54-7f38-7ba2-8dc3-5f90272d9f1a"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/apiacre-com-x402-preflight-checker-bc7fa9d9/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from apiacre.com](https://www.zero.xyz/host/apiacre.com/llms.txt)