Preflight

{
  "cached": false,
  "checked_at": "2026-09-23T17:00:00.000Z",
  "method": "GET",
  "options": [
    {
      "amount": "20000",
      "asset_symbol": "USDC",
      "index": 0,
      "network": "eip155:8453",
      "network_name": "Base",
      "pay_to": "0x6B0F4651eD42893ab58139938175E4a69f175F25",
      "payable": true,
      "problems": [],
      "usd": 0.02
    }
  ],
  "reasons": [],
  "recommended_option": 0,
  "safe_to_pay": true,
  "signals": {
    "advertised_price_usd": 0.02,
    "https": true,
    "listed_in_cdp_bazaar": false
  },
  "summary": "OK to pay: $0.02 on Base.",
  "url": "https://ichimoku-signal.fizzl.eu/signal/BTC-USDT",
  "verdict": "go"
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://x402-doctor.fizzl.eu/api/v1/preflight?max_usd=0.05&url=https%3A%2F%2Fichimoku-signal.fizzl.eu%2Fsignal%2FBTC-USDT'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - 'https://x402-doctor.fizzl.eu/api/v1/preflight?max_usd=0.05&url=https%3A%2F%2Fichimoku-signal.fizzl.eu%2Fsignal%2FBTC-USDT' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.001 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.001" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.001 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fx402-doctor.fizzl.eu%2Fapi%2Fv1%2Fpreflight
const res = await pay("https://x402-doctor.fizzl.eu/api/v1/preflight?max_usd=0.05&url=https%3A%2F%2Fichimoku-signal.fizzl.eu%2Fsignal%2FBTC-USDT");
console.log(res.status, await res.text());

# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.001 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.001"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.get("https://x402-doctor.fizzl.eu/api/v1/preflight?max_usd=0.05&url=https%3A%2F%2Fichimoku-signal.fizzl.eu%2Fsignal%2FBTC-USDT")
    print(res.status_code, res.text)