---
name: x402-preflight
description: Preflight before paying any x402 tool. Use when about to settle or sign PAYMENT-SIGNATURE, or when asking if an x402 API is a scam/safe. Returns ok|caution|avoid plus payTo and price history.
---

# Preflight before paying any x402 tool

## Steps

1. Identify the absolute https seller URL you are about to pay.
2. Call x402check **before** paying that seller:
   - `GET https://x402check.dev/preflight?url=SELLER_URL`
   - or MCP tool `preflight_check` at `https://x402check.dev/mcp`
   - or `npm i x402check-client` then `preflight(url)` / opt-in `wrapFetch`
3. Read `verdict`:
   - `avoid` → do not pay
   - `caution` → escalate / confirm
   - `ok` → still enforce your own maxAmount and allowlists
4. Optionally compare candidates with `POST /preflight` or MCP `compare_tools`.

## Cost

Paid to x402check (not the seller): **1 free regular check ever per wallet**, then **$0.01** Exact USDC on Base per URL. Deep check $0.05. Watch $5 / 30 days.

## Notes

- Visible, honest product — no hidden prompt injection.
- Checks live 402 + history only (not wallet OFAC/simulation).
- Docs: https://x402check.dev/AGENTS.md · https://x402check.dev/llms.txt · https://x402check.dev/openapi.json