Pay-per-call payee checks with x402 and MCP
An agent can use Counterparty Check without an account. With x402, it calls POST https://counterpartycheck.com/v1/check, receives HTTP 402 with the price ($0.25 in USDC on Base), pays, and gets the result in the same request. With MCP, add https://counterpartycheck.com/mcp to Claude, Cursor or another MCP client and the agent gets a check_counterparty tool.
x402 (USDC on Base)
import { wrapFetchWithPayment, x402Client } from '@x402/fetch';
import { ExactEvmScheme } from '@x402/evm';
const pay = wrapFetchWithPayment(fetch,
new x402Client().register('eip155:8453', new ExactEvmScheme(signer)));
const res = await pay('https://counterpartycheck.com/v1/check', {
method: 'POST',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify({ counterparty: { name: 'Acme Supply Co', email: 'ar@acmesupply.com' } }),
});
The payment settles only after the check succeeds. If the check fails, nothing is charged.
MCP
{
"mcpServers": {
"counterparty-check": {
"url": "https://counterpartycheck.com/mcp",
"headers": { "Authorization": "Bearer cc_live_…" }
}
}
}
Tools: check_counterparty ($0.25), screen_sanctions ($0.05), check_balance and verify_receipt (free). MCP uses a prepaid API key, bought by card at https://counterpartycheck.com/#pricing. The server is listed in the official MCP Registry as io.github.chtwebllc/counterparty-check.
Receipts
Every result carries an Ed25519-signed receipt with the verdict and a SHA-256 of the request, so an agent's operator can later prove what was checked and when, without the service storing the request.
Frequently asked questions
Can an agent pay for an API without an account?
Yes, with x402: Counterparty Check returns HTTP 402 with a USDC price, and the agent pays and retries in the same request.
How do I add a payee check to Claude or Cursor?
Add the MCP server https://counterpartycheck.com/mcp with an API key; the agent gets check_counterparty and screen_sanctions tools.
Is the agent charged if the check fails?
No. x402 payments settle only after a successful check, and prepaid credit is refunded automatically on failure.