ToolVet
75trust / 100

Watch

by factstamp.agentrails.workers.dev in Onchain & crypto

x402 APIPassing, checked 2 h ago

Buy a standing re-check of one citation or one package version, when an answer has to stay true rather than be true once: re-checked every day for 30 days. US$0.50 the month — 1.7 cents a check, under a 2-cent lookup. The first check is answered and signed on purchase, and each real change (a retraction, a new advisory, a yanked version) gets its own signed receipt. Pay per call here, or redeem a prepaid pack code (10 credits). Returns a read URL and a token shown once.

POST
https://factstamp.agentrails.workers.dev/watch
Price
$0.5
per call in USDC
Uptime
100%
last 30 days
Response time
335 ms
698 ms slowest 5%
Last check
Passed
2 h ago, next any minute now

Run a free test callHow to call it

Reliability

All checks passedSome failedAll failedNot checked

Status and outage history · Atom feed · Watch with other listings

How to call it

POST https://factstamp.agentrails.workers.dev/watch

Each call costs $0.5 in USDC on Base, paid with the request over x402.

Run a free test callOne unpaid request, the way an agent sends it. You see the payment challenge it gets back. Nothing is charged.

Example request

From the listing.

POST https://factstamp.agentrails.workers.dev/watch
content-type: application/json

{
  "kind": "citation",
  "subject": "10.1038/nature12373",
  "webhook": "https://example.com/factstamp/hook"
}

Example response

The provider's example. We can't check it without paying.

{
  "expires_at": "2026-11-05T06:30:00.000Z",
  "kind": "citation",
  "next_check_at": "2026-10-07T06:30:00.000Z",
  "paid_with": {
    "list_price_usd": 0.5,
    "rail": "x402_pay_per_call",
    "settlement": {
      "success": true
    }
  },
  "read_url": "https://factstamp.agentrails.workers.dev/watch/9f2c1ab4d0e57718",
  "receipt_url": "https://factstamp.agentrails.workers.dev/r/8bd1f0a4c9e27715",
  "seeded_verdict": "verified",
  "subject": "10.1038/nature12373",
  "token": "fw_9d1c… (shown once)",
  "watch_id": "9f2c1ab4d0e57718"
}

Call it from code

The curl command shows the payment challenge. The JavaScript and Python versions pay and call, and never pay more than $0.5.

curl: see the payment challenge
# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i -X POST 'https://factstamp.agentrails.workers.dev/watch' \
  -H 'content-type: application/json' \
  --data-raw '{"kind":"citation","subject":"10.1038/nature12373","webhook":"https://example.com/factstamp/hook"}'

# 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://factstamp.agentrails.workers.dev/watch' \
  -H 'content-type: application/json' \
  --data-raw '{"kind":"citation","subject":"10.1038/nature12373","webhook":"https://example.com/factstamp/hook"}' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode
JavaScript: pay and call
// 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 $0.5 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.5" });
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 $0.5 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Ffactstamp.agentrails.workers.dev%2Fwatch&method=POST
const res = await pay("https://factstamp.agentrails.workers.dev/watch", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    "kind": "citation",
    "subject": "10.1038/nature12373",
    "webhook": "https://example.com/factstamp/hook"
  }),
});
console.log(res.status, await res.text());
Python: pay and call
# 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 $0.5 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.5"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.post(
        "https://factstamp.agentrails.workers.dev/watch",
        json={
            "kind": "citation",
            "subject": "10.1038/nature12373",
            "webhook": "https://example.com/factstamp/hook",
        },
    )
    print(res.status_code, res.text)

Security scan

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