# QuickBuild x402 Preflight Check

> QuickBuild x402 Preflight Check is a paid API for AI agents from quickbuild.quynguyenbac.workers.dev, paid per call via x402, $0.005/call, status unknown (last checked 2026-11-04).

Validates whether a given x402-enabled endpoint is safe to pay, returning reachability, payment details, and a verdict before an agent commits funds

## Facts

- Endpoint: GET https://quickbuild.quynguyenbac.workers.dev/api/preflight?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-11-04
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/quickbuild-x402-preflight-check-4a67bd1a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_w_7fi9Tc8Ovasa4gpbvUm

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 quickbuild-x402-preflight-check-4a67bd1a
```

Example prompt: Before my agent pays anything, can you run a preflight check on https://quickbuild.quynguyenbac.workers.dev/api/domain to confirm it's a legitimate x402 endpoint — tell me the verdict, the USDC amount, and the wallet address it wants payment sent to?

## When to prefer this

Use this endpoint whenever an AI agent needs to validate an x402 pay-per-call URL before committing USDC — especially in automated pipelines where paying an unknown or malicious endpoint would be a security or financial risk. It is the right choice when you need to confirm the payTo address, network, and amount without actually executing a payment. Prefer this over blindly calling an x402 endpoint when the endpoint source is untrusted, when building agent guardrails, or when debugging x402 integration issues.

## Known failure modes

- Endpoint not reachable: reachable=false with HTTP error details
- URL does not return a 402: is_402=false, verdict likely do_not_pay
- Invalid or suspicious payTo address: payTo_valid=false, verdict risky or do_not_pay
- Non-USDC payment asset detected: asset_is_usdc=false flagged in checks
- Missing or malformed PAYMENT-REQUIRED header: challenge_source missing, verdict risky
- Input URL not provided or invalid format: 400 validation error
- Timeout or DNS failure on the target URL: reachable=false with latency spike

## How this service works

Pay-per-call web, AI and Base on-chain APIs for AI agents over x402 (USDC on Base, no account or API key), plus a free /ai-search ranking. Operated by an AI bot.

## Output

Returns a JSON object with: reachability status, HTTP status code, whether the endpoint returns a valid 402 challenge, an array of accepted payment options (asset contract, payTo address, network, USD amount), a verdict enum (safe_to_pay / risky / do_not_pay), human-readable reasons, an optional AI search ranking score if the host is indexed, redirect count, final URL after redirects, and latency in milliseconds.

## 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"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [],
     "properties": {
      "url": {
       "type": "string",
       "format": "uri",
       "pattern": "^https://",
       "description": "https URL of the x402 endpoint your agent plans to pay (public hostname, port 443)."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "required": [
      "url",
      "reachable",
      "http_status",
      "is_402",
      "accepts",
      "checks",
      "verdict",
      "reasons",
      "latency_ms"
     ],
     "properties": {
      "url": {
       "type": "string"
      },
      "paid": {
       "type": "boolean",
       "const": false
      },
      "checks": {
       "type": "array",
       "items": {
        "type": "object",
        "required": [
         "name",
         "pass",
         "reason"
        ],
        "properties": {
         "name": {
          "type": "string"
         },
         "pass": {
          "type": "boolean"
         },
         "reason": {
          "type": "string"
         },
         "severity": {
          "enum": [
           "fail",
           "warn",
           "info"
          ],
          "type": "string"
         }
        }
       }
      },
      "is_402": {
       "type": "boolean"
      },
      "method": {
       "enum": [
        "GET",
        "POST"
       ],
       "type": "string"
      },
      "accepts": {
       "type": "array",
       "items": {
        "type": "object",
        "properties": {
         "asset": {
          "type": "string"
         },
         "payTo": {
          "type": "string"
         },
         "scheme": {
          "type": [
           "string",
           "null"
          ]
         },
         "network": {
          "type": "string",
          "description": "CAIP-2, e.g. eip155:8453"
         },
         "amount_usd": {
          "type": [
           "number",
           "null"
          ]
         },
         "pay
… (truncated)
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "url": "https://quickbuild.quynguyenbac.workers.dev/api/domain",
  "paid": false,
  "is_402": true,
  "accepts": [
   {
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "payTo": "0x751a4c3841bE287544C371B4EE09Bd3366AeA7cf",
    "scheme": "exact",
    "network": "eip155:8453",
    "amount_usd": 0.003,
    "payTo_valid": true,
    "network_name": "Base",
    "amount_atomic": "3000",
    "asset_is_usdc": true
   }
  ],
  "reasons": [
   "valid x402 challenge; pay $0.003 USDC on Base to 0x751a4c3841bE287544C371B4EE09Bd3366AeA7cf"
  ],
  "verdict": "safe_to_pay",
  "ai_search": {
   "score": 92,
   "indexed": true,
   "sample_size": 40
  },
  "reachable": true,
  "latency_ms": 180,
  "http_status": 402,
  "x402_version": 2,
  "challenge_source": "PAYMENT-REQUIRED header"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/quickbuild-x402-preflight-check-4a67bd1a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from quickbuild.quynguyenbac.workers.dev](https://www.zero.xyz/host/quickbuild.quynguyenbac.workers.dev/llms.txt)