After our October 11 field test, the obvious question for any seller is: how do I check my own endpoint before a buyer does? So we built a way to do that.
Why we built it
x402 is a standard for paying for a web request with a crypto payment. A seller answers a request with a payment request (HTTP 402), the buyer pays, and the seller delivers. Every step has to work for money to move. Most sellers never see the buyer's side of it, so a broken endpoint can sit unnoticed.
We check the ERC-8004 agent economy every day. ERC-8004 is the on-chain list where AI agents register. Along the way we learned what breaks.
What we found in the weekly paid tests
Every week our own wallet makes a few small real purchases from agents, capped at $0.10 a request. In those tests, — of the — agents we have paid delivered what they sold. The last run was —.
The failures we wrote up on October 11 were specific and fixable:
- A login wall before the payment request. The seller answers with an error instead of a 402, so a buyer with no account cannot even see the price.
- A version mismatch. The payment request is written for one x402 version and the buyer speaks another.
- A payment service that rejects an ordinary USDC payment, often because the token name and version are missing and the buyer has to guess.
- No cheap route that shows a payment request, so an anonymous buyer has nowhere to start.
Details and fixes are in the field test.
How to use the check
- Free check, in seconds. Paste your URL at /seller-check. We send unpaid requests only and show what a buyer would see: the payment request, each payment option, the token details, and your discovery files. Nothing is paid.
- Full test, $0.50. We run the free check, make one real paid call to your endpoint at your listed price (up to $0.10), confirm the payment on Base, and send a report with what is broken and how to fix it. You can buy it from your own code or have an agent call the
seller_checktool on our MCP server. You get one free re-run within 7 days, so you can fix the problem and test again.
Paying for the test does not change any score. It is an independent snapshot of your endpoint on the day we ran it.