Assert

{
  "charged_usd": 0.005,
  "checks": 3,
  "ok": true,
  "passed": 3,
  "receipt": {
    "charter": "https://api.s2ar.dev/charter",
    "cost_usd": 0.005,
    "determinism": "replayable",
    "evidence_hash": "sha256:94abfed2…",
    "issued_at": "2026-10-10T00:00:00Z",
    "refund_rule": "failed calls are never charged",
    "what": "…",
    "witnesses": [
      "sym"
    ]
  },
  "record_sha256": "3f1c0d9e…",
  "results": [
    {
      "check": "json_valid",
      "evidence": {
        "type": "dict"
      },
      "ok": true
    },
    {
      "check": "required_keys",
      "evidence": {
        "missing": []
      },
      "ok": true
    },
    {
      "check": "citations_present",
      "evidence": {
        "min": 1,
        "urls": 1
      },
      "ok": true
    }
  ],
  "score": 1,
  "verdict": "pass"
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://api.s2ar.dev/x402/v1/assert?checks=%5B%7B%22check%22%3A%22json_valid%22%7D%2C%7B%22check%22%3A%22required_keys%22%2C%22keys%22%3A%5B%22summary%22%2C%22source_url%22%5D%7D%2C%7B%22check%22%3A%22citations_present%22%2C%22min%22%3A1%7D%5D&text=%7B%22summary%22%3A+%22The+glob+flag+is+parsed+in+defs.rs%22%2C+%22source_url%22%3A+%22https%3A%2F%2Fgithub.com%2FBurntSushi%2Fripgrep%22%7D'

# 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://api.s2ar.dev/x402/v1/assert?checks=%5B%7B%22check%22%3A%22json_valid%22%7D%2C%7B%22check%22%3A%22required_keys%22%2C%22keys%22%3A%5B%22summary%22%2C%22source_url%22%5D%7D%2C%7B%22check%22%3A%22citations_present%22%2C%22min%22%3A1%7D%5D&text=%7B%22summary%22%3A+%22The+glob+flag+is+parsed+in+defs.rs%22%2C+%22source_url%22%3A+%22https%3A%2F%2Fgithub.com%2FBurntSushi%2Fripgrep%22%7D' \
  | 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 $0.005 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.005" });
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 $0.005 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fapi.s2ar.dev%2Fx402%2Fv1%2Fassert
const res = await pay("https://api.s2ar.dev/x402/v1/assert?checks=%5B%7B%22check%22%3A%22json_valid%22%7D%2C%7B%22check%22%3A%22required_keys%22%2C%22keys%22%3A%5B%22summary%22%2C%22source_url%22%5D%7D%2C%7B%22check%22%3A%22citations_present%22%2C%22min%22%3A1%7D%5D&text=%7B%22summary%22%3A+%22The+glob+flag+is+parsed+in+defs.rs%22%2C+%22source_url%22%3A+%22https%3A%2F%2Fgithub.com%2FBurntSushi%2Fripgrep%22%7D");
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 $0.005 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.005"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.get("https://api.s2ar.dev/x402/v1/assert?checks=%5B%7B%22check%22%3A%22json_valid%22%7D%2C%7B%22check%22%3A%22required_keys%22%2C%22keys%22%3A%5B%22summary%22%2C%22source_url%22%5D%7D%2C%7B%22check%22%3A%22citations_present%22%2C%22min%22%3A1%7D%5D&text=%7B%22summary%22%3A+%22The+glob+flag+is+parsed+in+defs.rs%22%2C+%22source_url%22%3A+%22https%3A%2F%2Fgithub.com%2FBurntSushi%2Fripgrep%22%7D")
    print(res.status_code, res.text)