# Sentinel 24-Hour URL Watcher

> Sentinel 24-Hour URL Watcher is a paid API for AI agents from sentinel.rootstuff.io, paid per call via x402, $0.5/call, status unknown (last checked 2026-09-15).

Monitors a public URL for 24 hours and delivers signed webhook callbacks whenever its availability/verdict changes

## Facts

- Endpoint: GET https://sentinel.rootstuff.io/x402/watch-24h
- Price: $0.5/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/sentinel-24-hour-url-watcher-8eb3f546
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_TGI56v9_vtp9onIVQr7Tm

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability sentinel-24-hour-url-watcher-8eb3f546
```

Example prompt: Watch https://api.myservice.com/health for the next 24 hours and POST a signed callback to https://hooks.myapp.com/sentinel whenever its verdict changes — include {"service":"api-health-check"} in every callback.

## When to prefer this

Choose this endpoint when you need extended 24-hour continuous monitoring of a public URL with webhook-based notifications, rather than a one-off check or short-term watch. Prefer it over the 1-hour sibling when you need longer coverage — e.g. monitoring a deployment overnight or tracking a vendor API across a full business day. Prefer it over single-point checks (ping, headers, TLS) when you care about changes over time rather than a snapshot. The signed callbacks make it suitable for automated pipelines that need tamper-evident notifications.

## Known failure modes

- Invalid or non-public target URL — private IPs or reserved addresses rejected
- Callback URL is private, uses a reserved address range, or follows redirects — request refused
- Payload exceeds 4 KB limit — request rejected
- Target URL becomes permanently unreachable — no further callbacks sent after failure
- Callback URL is unresponsive — delivery may be retried but not guaranteed
- Malformed URL schema (non-http/https) — rejected at validation

## How this service works

Watch a URL for 24 hours: signed callbacks when its verdict changes

## Output

The endpoint registers the watch job and returns a confirmation. Over the next 24 hours, whenever the monitored URL's verdict (up/down/availability status) changes, Sentinel POSTs a signed callback to the specified callback_url. Each callback includes the verdict change details and echoes back the custom payload (up to 4 KB) provided at registration. Callbacks are cryptographically signed so recipients can verify authenticity.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "description": "The http(s) URL to watch. Public hosts only."
  },
  "payload": {
   "type": "object",
   "description": "Up to 4 KB of JSON echoed back in every callback."
  },
  "callback_url": {
   "type": "string",
   "description": "Public https URL that receives the POSTs. Private and reserved addresses are refused; redirects are not followed."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/sentinel-24-hour-url-watcher-8eb3f546/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from sentinel.rootstuff.io](https://www.zero.xyz/host/sentinel.rootstuff.io/llms.txt)