# Foundry x402 Preflight Checker

> Foundry x402 Preflight Checker is a paid API for AI agents from minty-sprout.onrender.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-11-01).

Probes a paid x402 endpoint unpaid, parses the payment-required response, and lints every payment option for validity, returning an ok/warn/block verdict with detailed reasons.

## Facts

- Endpoint: POST https://minty-sprout.onrender.com/v1/x402-preflight?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-11-01
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/foundry-x402-preflight-checker-e15c4ee7
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_4-DYj77H_zBiAYAcnNXrQ

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 foundry-x402-preflight-checker-e15c4ee7 -d '<json body>'
```

Example prompt: Before my agent pays it, run a preflight check on the x402 endpoint at https://api.example.com/v1/data — tell me if the payTo address, USDC network, and EIP-712 domain all look safe, and whether it gets an ok, warn, or block verdict.

## When to prefer this

Use this endpoint when an AI agent or developer needs to vet an x402 pay-per-call API before committing a payment signature. It is the right choice when you want deterministic, rule-based linting (no LLM hallucination risk) of all payment parameters including network, USDC contract address, EIP-712 domain, payTo address, amount, and timeout. Prefer it over manual inspection when building agent workflows that autonomously discover and pay x402 APIs and need a safety gate before signing.

## Known failure modes

- Target URL is unreachable or times out — returns error with latency and no options
- Target URL does not return a 402 status — verdict may be block with explanation
- Malformed x402 payment-required body or header — issues listed per field
- Zero or invalid payTo address detected — flagged as block-level issue
- Testnet network detected when mainnet expected — flagged as warn or block
- Input URL missing or malformed — returns validation error

## How this service works

x402 preflight: checks a paid x402 endpoint before a payment is signed. Probes it unpaid, parses the v1 body or v2 PAYMENT-REQUIRED header, lints every accepts[] option (network, canonical USDC, EIP-712 domain name/version that signatures verify against, EIP-55 payTo, zero payTo, amount, timeout, testnet, resource host) and returns ok/warn/block with reasons. Input: URL, optionally 'POST <url>'. Deterministic, no LLM.

## Output

Returns a JSON object with: the probed URL, HTTP method used, response status code, x402 version detected, overall verdict (ok/warn/block), latency in ms, a list of top-level issues, and a per-option breakdown including scheme, network, payTo address, amount in USD, asset symbol, EIP-712 validation results, and option-level issues and verdict. Also flags bazaar_extension if present.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "input": {
   "type": "string",
   "maxLength": 8000,
   "description": "URL of a paid x402 endpoint, optionally prefixed with GET or POST, e.g. \"POST https://api.example.com/v1/x\""
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "url": "https://x402-preflight.nextill-pos.workers.dev/v1/preflight",
  "issues": [],
  "method": "GET",
  "status": 402,
  "options": [
   {
    "issues": [],
    "pay_to": "0xB3cDDccEe6B150c8efFD55B961afc0Ecefe7f247",
    "scheme": "exact",
    "network": "eip155:8453",
    "verdict": "ok",
    "price_usd": 0.003,
    "asset_symbol": "USDC"
   }
  ],
  "verdict": "ok",
  "latency_ms": 1001,
  "x402_version": 2,
  "bazaar_extension": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/foundry-x402-preflight-checker-e15c4ee7/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from minty-sprout.onrender.com](https://www.zero.xyz/host/minty-sprout.onrender.com/llms.txt)