# NOVA Monitor Check

> NOVA Monitor Check is a paid API for AI agents from nova-demand-worker.vercel.app, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-11).

Checks a web page element for content changes by comparing a SHA-256 hash of the selected content against a previous hash

## Facts

- Endpoint: POST https://nova-demand-worker.vercel.app/x402/monitor-check?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/nova-monitor-check-e9c0df52
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_G1mSDcOCubN3hmIpUztAM

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 nova-monitor-check-e9c0df52 -d '<json body>'
```

Example prompt: Check if the main headline on https://example.com/news has changed since last time — use the selector 'h1.headline' and compare against my previous hash 'sha256abc123'.

## When to prefer this

Use this endpoint when you need a lightweight, pay-per-call web content change detector that hashes a specific CSS-selected element rather than the entire page. Ideal for agents that need to poll a URL periodically and only act when something has actually changed, without storing full page snapshots.

## Known failure modes

- Invalid or unreachable URL returns an error
- CSS selector matches no elements, resulting in empty or null hash
- Network timeout if the target page is slow to load
- Invalid previousHash format may cause comparison failure
- Payment failure via x402/USDC will block the request

## How this service works

Machine-facing pay-per-call utility services using x402 on Base with USDC.

## Output

Returns a JSON object containing a SHA-256 hash of the current content at the selected element, a 'changed' boolean indicating whether it differs from the previousHash, and a 'checkedAt' ISO timestamp of when the check was performed.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string"
  },
  "selector": {
   "type": "string"
  },
  "previousHash": {
   "type": [
    "string",
    "null"
   ]
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "hash": "sha256...",
  "changed": null,
  "checkedAt": "2026-09-24T00:00:00.000Z"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/nova-monitor-check-e9c0df52/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from nova-demand-worker.vercel.app](https://www.zero.xyz/host/nova-demand-worker.vercel.app/llms.txt)