Builders & sellers

Keep agents paying you.
Watch drift before they skip you.

If your public listing drifts from your live 402 challenge, your endpoint goes down, or your payTo wallet changes, agents that preflight with x402check may refuse to pay or choose another tool. Those signals are heuristics about the endpoint · not a legal accusation. x402check helps you monitor the same signals and prove ownership.

Watch your endpoint Verify ownership Agent preflight

Watch · $5 for 30 days

One prepaid Exact USDC payment on Base buys 30 days of daily re-checks for one seller URL. Watch does not auto-renew. After expiry, monitoring stops unless you manually pay again via POST /watch/renew (another $5 for another 30 days).

Alerts fire to an HTTPS webhookUrl and/or email when payTo, price, network, or availability changes from the baseline set at purchase.
Status is free: GET /watch?id=… (contact details are redacted on status).
Same Base USDC rails as agent preflight · paid to x402check, not to your buyers.

Buy with HTTP

POST https://x402check.dev/watch
Content-Type: application/json
PAYMENT-SIGNATURE: <Exact USDC on Base for $5>

{"url":"https://yours.example/x402","webhookUrl":"https://hooks.example/x402check","email":"you@example.com"}

Unauthenticated calls return HTTP 402. Decode PAYMENT-REQUIRED, sign Exact USDC on Base, retry with PAYMENT-SIGNATURE. Optional fields: webhookUrl (https) and/or email.

Buy with MCP

tools/call · watch_tool
{"url":"https://yours.example/x402","webhookUrl":"https://hooks.example/x402check","email":"you@example.com"}
# unpaid call returns PaymentRequired; retry with params._meta["x402/payment"]

Full agent docs: /docs · OpenAPI: /openapi.json · MCP: /mcp.json.

Verify ownership & badge

Prove you control an endpoint, then view only that endpoint’s private periodic snapshot. Snapshots are not a public scanner dataset and are not a substitute for a live paid /preflight ($0.01).

Primary: sign a challenge with the endpoint’s live payTo wallet (EIP-191; ERC-1271 smart wallets supported).
Fallback: publish a short-lived token as DNS TXT x402check-verify=… or at /.well-known/x402check-verify.txt.
Optional opt-in Verified by x402check badge: unguessable id at /badge/<id>.svg, shown when your latest snapshot is pass; revocable anytime.

How verify works Open owner dashboard

Agents still check before they pay

Buyers and agents call GET /preflight?url=… (or MCP preflight_check) for $0.01 Exact USDC and get an ok / caution / avoid verdict plus history for that URL. Keeping your live challenge stable and your endpoint reachable is how you stay payable.