SiteCheck README

SiteCheck: pay-per-call tools for AI agents (x402 on Base, Solana and Arc)

Live: https://api.sitecheck-api.workers.dev · listed on x402scan, the official MCP Registry (io.github.bck-stack/sitecheck), Smithery and mcpservers.org · MCP: /mcp · discovery: /.well-known/x402, /openapi.json

SiteCheck is a small API that AI agents can use without an account or API key: 29 pay-per-call tools in all. Besides its AI and web tools (including a web page to Markdown reader), it sells PDF to text, translation, tech stack detection, sitemap URLs, exchange rates, e-mail, domain and Solana token and wallet data, business and compliance data (EU VAT, IBAN, LEI, US recalls, OSHA/EPA enforcement, UK insolvency notices), prediction-market data and unsigned trade transactions powered by Panta. Every call is paid per request in USDC with the x402 protocol, on Base, Solana or Arc (Circle's L1), whichever the buyer holds USDC on. Call it, get a 402 Payment Required listing the price on each network, sign the payment and get the result. It runs on Cloudflare Workers and Workers AI.

Prediction markets (Panta)

Agents can buy market intelligence and ready-to-sign trade transactions per call, with no account and no API key. An agent researching an event pays a fraction of a cent to find the markets and one cent for a market's odds and a neutral brief. An agent that wants to act pays for an unsigned Panta buy transaction and signs it with its own wallet. Panta runs USDC prediction markets on Solana.

• No custody. SiteCheck never signs, holds keys or custodies funds. build-buy hands back an unsigned transaction whose only signer is the agent's wallet.
• Information only, not financial advice. Every response says so (disclaimer), and the brief never recommends a trade. If the model's text reads like advice, a factual template is returned instead.
• Powered by Panta. Every response carries poweredBy: { text: "Powered by Panta", url: "https://panta.market" }, as Panta's Terms of Use require.
• Pay only for results, as with every tool: if Panta refuses or fails, the call returns an error and nothing is settled. The catalog is cached for 45 seconds and prices for 15 seconds, and responses say how old their data is.
• The tools are on only when the PANTA_API_KEY secret is set. Otherwise they are hidden, and GET /health says why. Endpoints, shapes, attribution and open questions: docs/PANTA.md.

node scripts/demo-markets.mjs --q bitcoin            # search, brief and quote, paid on Solana (~0.017 USDC)
node scripts/demo-markets.mjs --q bitcoin --build    # also builds the unsigned transaction (+0.01); never signs or sends it

Web, documents, e-mail, domain and Solana data

Business and compliance data

Six tools for an agent that has to check a counterparty before it trades with it. All of them read free official sources (or our own cache of one), need no key from the caller, and follow the same rule as every route here: a call that fails (bad input, upstream down, timeout) returns 4xx/5xx and is not settled, so the buyer is not charged.

Workers limits are respected: every upstream call has a timeout (at most 10 s) and a SiteCheck/1.x User-Agent, every tool stays well under 50 subrequests, and nothing large is parsed per request (the Gazette text is scanned and only matching notices are parsed). Stable upstream answers are cached with the Cache API where it works.

curl -s "https://api.sitecheck-api.workers.dev/api/vat?number=DE811907980"        # 402 first: pay with any x402 client

MCP server

https://api.sitecheck-api.workers.dev/mcp is a remote MCP server (Streamable HTTP, stateless, JSON answers). Every paid endpoint is an MCP tool with the same input schema (read, pdf, tech, email_check, domain, solana_token, vat, lei, ...), and the same price.

Payment uses the x402 MCP transport: a tools/call without payment returns isError with the x402 PaymentRequired object in structuredContent; the client signs one option and repeats the call with the PaymentPayload in params._meta["x402/payment"]; the answer carries the settlement in result._meta["x402/payment-response"]. A tool call that fails is not settled. Each call is replayed inside the Worker against the matching /api route, so MCP and HTTP buyers go through the same payment checks.

import { createx402MCPClient } from "@x402/mcp";
import { ExactEvmScheme } from "@x402/evm/exact/client";
import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js";

const client = createx402MCPClient({
  name: "my-agent", version: "1.0.0",
  schemes: [{ network: "eip155:8453", client: new ExactEvmScheme(account) }], // a viem account holding USDC on Base
  autoPayment: true,
});
await client.connect(new StreamableHTTPClientTransport(new URL("https://api.sitecheck-api.workers.dev/mcp")));
const page = await client.callTool("read", { url: "https://docs.x402.org/introduction" }); // pays $0.002

MCP clients without x402 support (for example a plain remote connector) can list the tools and see each price, but a call returns the payment requirements instead of a result.

Networks

The price is the same on every network. Buyers need only USDC: EVM payments are EIP-3009 signatures, and the facilitator pays gas and Solana fees. Sources and design decisions: docs/NETWORKS.md.

Try it

curl -si "https://api.sitecheck-api.workers.dev/api/audit?url=example.com" \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 -d
# {"x402Version":2,"error":"Payment required", ..., "accepts":[{ "network":"eip155:8453", "amount":"20000", ... }, ...]}

Pay with any x402 client. Base or Arc, with @x402/fetch and a viem account:

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

const account = privateKeyToAccount(process.env.EVM_PRIVATE_KEY);  // holds a little USDC
const client = x402Client.fromConfig({
  schemes: [{ network: "eip155:8453", client: new ExactEvmScheme(account) }],   // Arc: "eip155:5042"
  // Arc only: its USDC is not in @x402/evm's built-in asset list yet, so opt in (cap: $0.10 per call).
  // spendControls: { allowedAssets: [{ network: "eip155:5042", asset: "0x3600000000000000000000000000000000000000", maxAmountPerPayment: "100000" }] },
});
const pay = wrapFetchWithPayment(fetch, client);
const res = await pay("https://api.sitecheck-api.workers.dev/api/audit?url=example.com");
console.log(await res.json());

Solana, with @x402/svm and a @solana/kit signer:

import { readFileSync } from "node:fs";
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { ExactSvmScheme } from "@x402/svm/exact/client";
import { createKeyPairSignerFromBytes } from "@solana/kit";

const signer = await createKeyPairSignerFromBytes(Uint8Array.from(JSON.parse(readFileSync("buyer.json", "utf8"))));
const client = new x402Client().register("solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp", new ExactSvmScheme(signer));
const pay = wrapFetchWithPayment(fetch, client);
console.log(await (await pay("https://api.sitecheck-api.workers.dev/api/audit?url=example.com")).json());

Every endpoint declares its input schema and an output example through the x402 Bazaar discovery extension, so agents can find and call it without reading docs.

Demo agent

scripts/demo-agent.mjs discovers the API through /.well-known/x402, pays for one audit on the network you pick, and prints the result and the transaction link:

node scripts/demo-agent.mjs --network base     # or arc, solana

On the first run it creates a throwaway wallet in a git-ignored file (.env.evm for Base and Arc, .env.solana for Solana) and prints its address. Fund it with about 0.10 USDC on that network; one audit costs 0.02 USDC, and no ETH or SOL is needed. --dry-run stops before paying, and --url points it at another deployment.

Design notes

• Pay only for results. The settlement runs after the handler. If a model or upstream fails, the handler returns an error status and the payment is not settled, so the buyer isn't charged. This holds on all three networks and is covered by the tests.
• One route, several networks. Each route lists one x402 accepts entry per configured network. Base and Solana settle through PayAI. Arc settles through Circle's Facilitator Service on its keyless trial: each request carries a seller proof signed by the Arc receiving wallet's key (see below). Each facilitator client only reports the networks assigned to it (lib/payments.js).
• Workers-safe x402 middleware. A Worker can't await a promise created by another request, and the x402 middleware initialises lazily. Each request builds and initialises its own middleware until one has finished; that one is then reused (lib/app.js).
• No keys in the repo. Receiving addresses live in wrangler.toml [vars] (empty by default). The Arc seller key (or, as a fallback, the Circle API key) is a Worker secret. The helper scripts keep their wallets in git-ignored .env.* files.

Arc: Circle's keyless trial and a hot wallet

Circle's Facilitator Service normally needs an API key, and on mainnet that needs a Circle account with a credit card on file. SiteCheck uses Circle's keyless trial instead. Every /verify and /settle request carries a Facilitator-Seller-Proof header: an EIP-712 signature by the key that controls Arc's payTo, bound to the route, the exact request body and a fresh nonce (lib/sellerProof.js, lib/circle.js).

The trade-off: that key has to live in the Worker, as the secret ARC_SELLER_KEY. So Arc's payTo is a dedicated hot wallet that only receives payments. The owner sweeps it to a cold wallet regularly (scripts/sweep-arc.mjs), so a leaked key would expose at most what came in since the last sweep. The trial allowance is also limited, and Circle doesn't publish it. When it runs out, Circle answers 403 registration_required. The payment is not settled and the buyer is not charged, the Worker logs it, and GET /health shows arc.trialExhausted: true. From then on, Arc needs a Circle API key or has to be switched off. Details: docs/NETWORKS.md.

Run your own

npm install
npm test                    # no network needed: the facilitators and Panta are mocked
npx wrangler dev            # local

Deploy: set account_id and at least one receiving address in wrangler.toml (or pass it with --var). For Arc, create the hot wallet and store its key first:

node scripts/new-arc-wallet.mjs            # Arc only: prints the new address; the key goes to .env.arc-seller
npx wrangler secret put ARC_SELLER_KEY     # paste the key from .env.arc-seller
npx wrangler secret put PANTA_API_KEY      # optional: a pk_live_... key switches the prediction-market tools on
npx wrangler secret put DOL_API_KEY        # optional: switches OSHA on in /api/violations
npx wrangler secret put COMPANIES_HOUSE_API_KEY   # optional: enriches /api/uk-insolvency rows
npx wrangler deploy
node scripts/sweep-arc.mjs --to 0xYourColdWallet          # later, regularly: shows what it would send
node scripts/sweep-arc.mjs --to 0xYourColdWallet --yes    # sends it

Leave an address empty to switch that network off. GET /health shows which networks are active and why the others are not, and whether the Panta tools are on. For Arc it also shows the auth mode, the receiving address and the trial status.

License

MIT

Mainnet transactions

Real x402 settlements on all three networks:

• Solana (our test): https://solscan.io/tx/4DQcTjw791d83iUFU7NBbyi3JZxXsvHbNHWgcXb9eeVT4tqReDV4ZFqYanUpJXnGP2ogucsWHqehioJd6Dq1ghDJ
• Base (our test): https://basescan.org/tx/0xf4e4a1aeeff698706e49cd921321cda9dba79babefd00b624bdf836fda57beb1
• Arc (our test): https://explorer.arc.io/tx/0xb6abceb6108099730c31b00f9140288585a869029bc5c922b88f0df5e8289476
• Base, paid by an outside AI agent we don't control (one of its 12 paid calls so far): https://basescan.org/tx/0x9e37d0287f04f7c1f89f159f839c0f391230dab6c21aeead58d6a29588239ea9
• Base, paid by a second outside wallet (6 Oct 2026): https://basescan.org/tx/0x9d5f1cae2c5016f165eead7dc56f51a3d74a1ea90a06270d4b0ca8bf97d8d211