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QuickBuild x402 Preflight Check
x402
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
Price / call$0.005
Success—
StatusUnknown
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.
Example use cases
Pre-payment safety audit for agent
“My AI agent is about to pay an x402 endpoint at https://some-api.example.com/data — can you run a preflight check first and tell me if it's safe to pay, what address it's sending USDC to, and how much?”
Discovering payment details for unknown API
“I found this URL that supposedly accepts x402 payments: https://api.thirdparty.com/search — can you check whether it's reachable, actually returns a 402, and what the payment terms are before I wire any USDC?”
Validating x402 endpoint in agent pipeline
“Before we wire up this new pay-per-call tool in our agent pipeline, check https://quickbuild.quynguyenbac.workers.dev/api/crypto-prices and confirm the verdict is safe_to_pay, the asset is USDC on Base, and the payTo address looks valid.”
Technical details
Endpoint
GEThttps://quickbuild.quynguyenbac.workers.dev/api/preflight?utm_source=zero.xyzWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"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"
}
}Tags
x402
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