Probe

{
  "amount_base_units": "20000",
  "answer": {
    "claim": "Australia's cash rate target is 3.60%",
    "receipt": {
      "alg": "Ed25519",
      "canonical": "<the exact bytes that were signed>",
      "key_id": "<the key_id printed on this door's 402, and found in the published key set>",
      "payload": {
        "alg": "Ed25519",
        "answer_hash": "<sha256 of the canonical served answer, minus `paid_with` and minus `answer.receipt`>",
        "issued_at": "2026-10-22T01:02:03.000Z",
        "issuer": "https://agents.factstamp.dev",
        "key_id": "<the same key_id>",
        "sources": [
          {
            "http_status": 200,
            "licence": "",
            "source": "Reserve Bank of Australia",
            "url": "https://www.rba.gov.au/statistics/cash-rate/"
          }
        ],
        "subject": "Australia's cash rate target is 3.60%",
        "tool": "probe_claim",
        "v": 1,
        "verdict": "verified"
      },
      "sig": "<base64url signature over `canonical`>"
    },
    "verdict": "verified"
  },
  "claim": "Australia's cash rate target is 3.60%",
  "kind": "figure",
  "list_price_usd": 0.02,
  "paid_with": {
    "list_price_usd": 0.02,
    "rail": "x402_pay_per_call"
  },
  "probe": true,
  "retrieved_at": "2026-10-22T01:02:03.000Z",
  "source": {
    "data_as_of": "2026-08-01",
    "http_status": 200,
    "licence": null,
    "name": "Reserve Bank of Australia",
    "retrieved_at": "2026-10-22T01:02:03.000Z",
    "url": "https://www.rba.gov.au/statistics/cash-rate/"
  },
  "tier": "probe",
  "unknown": false,
  "value": 3.6,
  "verdict": "verified"
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i -X POST 'https://agents.factstamp.dev/probe' \
  -H 'content-type: application/json' \
  --data-raw '{"claim":"Australia'\''s cash rate target is 3.60%","kind":"figure"}'

# 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 - -X POST 'https://agents.factstamp.dev/probe' \
  -H 'content-type: application/json' \
  --data-raw '{"claim":"Australia'\''s cash rate target is 3.60%","kind":"figure"}' \
  | 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 $0.02 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.02" });
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 $0.02 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fagents.factstamp.dev%2Fprobe&method=POST
const res = await pay("https://agents.factstamp.dev/probe", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    "claim": "Australia's cash rate target is 3.60%",
    "kind": "figure"
  }),
});
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 $0.02 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.02"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.post(
        "https://agents.factstamp.dev/probe",
        json={
            "claim": "Australia's cash rate target is 3.60%",
            "kind": "figure",
        },
    )
    print(res.status_code, res.text)