X402 Listing Monitor MCP Server

x402 Bazaar Listing Monitor

Scheduled watchdog for x402 sellers: polls Coinbase CDP's public Bazaar discovery catalog for the resources you register and alerts when one drops out or comes back — instead of finding out from a revenue dip days later.

Sellers who settle real x402 payments have no reliable way to confirm their resources stay discoverable in CDP's Bazaar catalog. The discovery API has a recurring, publicly-reported class of bug where a resource silently stops appearing despite confirmed settlements — sellers currently catch this only by manually re-running GET /discovery/merchant?payTo=<address> on their own schedule.

This service automates that check: register your payTo address and the resource URLs you serve, and a scheduled poll diffs them against the live discovery catalog. State changes are recorded with timestamps, so you have a durable history you can cite if you need to escalate to CDP support.

MCP server

Endpoint: https://x402-listing-monitor.acjlabs.com/mcp (streamable HTTP)

One tool — no signup, no API key:

check_listing_health

Checks whether a seller's x402 Bazaar resources are currently listed under a given payTo address in the public discovery catalog. Runs the same per-seller diff as the scheduled poller, on demand, for any payTo/resources pair — registered here or not.

Returns each resource flagged as listed or missing, as JSON.

HTTP API

Base URL: https://x402-listing-monitor.acjlabs.com

POST /register

{
  "sellerId": "your-slug",
  "payTo": "0x0000000000000000000000000000000000000000",
  "resources": ["https://api.example.com/your-resource"],
  "alertWebhookUrl": "https://example.com/hook"
}

• sellerId — 2–64 characters: letters, digits, -, _
• payTo — 0x-prefixed, 40 hex characters
• resources — 1–200 http(s) URLs, no duplicates
• alertEmail / alertWebhookUrl — optional; a webhook URL must be https

Resources are watched by self-declaration: the service checks what you tell it to check. A sellerId that already exists is rejected rather than overwritten.

Per-IP rate limits apply to /register and /poll.

Polling and alerts

The scheduled poll runs every 6 hours. Each run diffs your registered resources against the live discovery catalog and records state changes with timestamps — a history, not just a point-in-time answer.

Paid tiers also tighten the polling interval.

Status

Early release. The service is live and polling, and the recorded alert history is authoritative for what it has observed. Outbound alert delivery is not enabled yet — state changes are detected and persisted; delivery is the next thing being wired.

Source availability & support

This repository hosts the documentation for the hosted service. The service implementation is not open source. Bug reports and feature requests are welcome in this repo's Issues; you can also reach us at contact@acjlabs.com.