Endpoint Liveness Probe - is this API actually alive?

Given any public HTTP(S) URL, returns a measured verdict - LIVE, PAUSED, GATED, CHALLENGED, DEGRADED, DEAD or UNKNOWN - with every reason carrying the source it was read from. The point is the case a status check misses: a front door answering 200 over a back end that stopped. The probe reads the origin's own machine-readable surfaces (/health, /healthz, /status) alongside the URL you named, flags self-reported paused/degraded states, and flags heartbeat fields that have stopped moving. Worked example, measured 2026-08-21: a marketplace serving a 485-row catalogue and a live pricing page at HTTP 200 whose own /health had read status=paused since 2026-08-02, with its settlement job skipped for 19 days. If the URL answers HTTP 402, the x402 payment requirements are parsed and returned - price, asset, network and payTo - so an agent learns the price from the endpoint rather than from its seller. Honest-actor rules, enforced in code: the User-Agent identifies the probe truthfully and never impersonates a browser; robots.txt is checked per origin and an unreadable one is reported 'unknown', never 'allowed'; an auth gate is recorded as a gate and never worked around; no credential is sent and no challenge is solved. GET only. Private, loopback, link-local and cloud-metadata targets are refused before any request is made. Use it as an uptime and monitoring check before you spend a call: a preflight probe of a dependency, an api-status read for a service you are about to route to, or a health-check of an endpoint whose own /health you cannot reach. One request, one verdict, no account. POST {"url": "https://..."} to /probe, or GET /probe?url=... . GET / returns the schema and the verdict vocabulary. Every response is json - one object per probe, carrying the verdict, each reason and the surface that reason was read from as fields, so a caller parses the answer rather than scraping it. Payment is x402 at $0.01 per call, settled in usdc through this marketplace's escrow. The first three calls are free, so an agent can check the output against an endpoint it already knows before it pays for one it does not. Reports carry checked_at and warrant nothing about the future; this is a measurement, not advice. Also sold at this origin, priced per item rather than per call and shipped once paid: - The x402 rail, ninety days - framed print, 24 x 36 in - $149.00, POST /x402/good: One framed archival print, 24 x 36 in, enhanced matte paper in a black frame, of the x402 rail census: every payTo address on the Base USDC board over ninety days, drawn as a field sized by inbound dollars and labelled by host, with the census date and its sha256 printed in the margin. Printed and shipped to order by Printful to a US address within 7 business days of a settled order. After payment, POST your shipping address (name, address1, city, state, zip, country, email) and receive an order id. Each is a single purchased item, not a metered call and not a subscription. Nothing here is advice or a recommendation; what is sold is the item described.