Check a Seller Before Your Agent Pays It

An agent that pays over x402 has two facts about a new seller: a price and an address. Public payment data adds a third.

Key takeaways

• The Agent GDP seller check returns 30 days of public payment data for a domain, wallet or service name: organic revenue, organic share, buyers, repeat buyers, the largest buyer's share, the last paid day and a measured level.
• It costs $0.01 per call over x402 and is listed in the x402 Bazaar. In MCP clients it is a free tool, check_seller_before_paying.
• The npm package @agentgdp/check-before-pay runs the check automatically before an agent pays a new payee, once per 24 hours and only for payments from $0.10. It never blocks unless you set a rule.
• A level describes payments, not companies. The rules are public on the methodology page.

Why check a seller before paying

An agent that pays over x402 decides in milliseconds whether to send money to a wallet it has never seen. The 402 answer tells it the price and the receiving address. It does not tell it whether anyone else pays that address, whether those buyers come back, or whether most of the money comes from one wallet.

Those questions have answers in public chain data. Agent GDP indexes x402 and MPP payments and separates organic revenue, money from independent buyers, from payments that do not pass its screen.

What the seller check returns

Pass a domain, a wallet address or a service name. A real answer from 11 November 2026, for a media API:

Read plainly: all revenue passes the organic screen, every buyer came back, and no single buyer dominates. The level says the buyer base is small, not that something is wrong.

Three ways to use it

1. One x402 call, $0.01. Paid in USDC on Base. The endpoint is listed in the x402 Bazaar.

GET https://agentgdp.io/api/v1/x402/check?q=<domain|wallet|name>

2. Every new payee, automatically. The npm package wraps your x402 fetch. Source and tests: github.com/DenisTheM/check-before-pay (MIT).

npm i @agentgdp/check-before-pay

import { withSellerCheck, blockLowOrganic } from "@agentgdp/check-before-pay";

// Checks each new payee once per 24 hours, for payments from $0.10.
// Without a policy it only reports; this one blocks below 20% organic.
const pay = withSellerCheck(paidFetch, { policy: blockLowOrganic(0.2) });

3. In an MCP client, free. Add the server and call the tool check_seller_before_paying.

https://agentgdp.io/api/mcp

People can run the same check on the website at agentgdp.io/check.

What a level is not

The check reads public payments over 30 days. It does not know who runs a wallet, whether a buyer is an agent or a script, or what a business is worth. It is not a credit rating and not investment advice. Only sellers that present themselves publicly get a level; others get figures only. Payments to Agent GDP's own wallet are left out of every Agent GDP total.

Disclosure: Agent GDP sells the paid check described here. Payments to Agent GDP are left out of every published total.