# how.is Page Change Watcher

> how.is Page Change Watcher is a paid API for AI agents from how.is, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-31).

Monitors a public URL for content changes, storing a baseline on first call and returning a text diff with change percentage on subsequent calls.

## Facts

- Endpoint: POST https://how.is/v1/watch/page?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-31
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/how-is-page-change-watcher-1b44b645
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_R2g8o_yHfKHrlpdc08ViB

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 how-is-page-change-watcher-1b44b645 -d '<json body>'
```

Example prompt: Check if https://example.com/pricing has changed since the last time you looked at it — tell me what was added or removed and what percentage of the page changed.

## When to prefer this

Choose this endpoint when you need lightweight, pay-per-call change detection on individual public URLs without setting up recurring infrastructure. It is ideal for agents that need to check whether a specific page has changed since a previous check, get a human-readable text diff with added/removed content, and receive a quantified change percentage — all in a single API call with no subscription or webhook setup required.

## Known failure modes

- URL is not publicly accessible or returns non-200 status
- First call only stores baseline — no diff returned until a second call is made
- URL behind authentication or bot-blocking returns empty or error content
- Change percentage below 2% threshold is not reported as a change
- Invalid or malformed URL returns validation error
- Rate limiting or network timeouts on slow-loading pages

## How this service works

Has this page changed since your last call, and how much? The first call stores a baseline; later calls return a text diff (2% threshold).

## Output

A JSON object containing: a boolean indicating whether the page changed, the percentage of content that changed, the text that was added, the text that was removed, the timestamp of the last detected change, and a receipt confirming the x402 micropayment of $0.005 USDC. On the first call, a baseline is stored and no diff is available yet.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "format": "uri",
   "description": "An http(s):// URL on the public internet"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "data": {
   "_shape": "data with baseline, changed, change_pct, added, removed, last_change_ts."
  },
  "result": "Page-change watch for the requested subject",
  "receipt": {
   "rail": "x402",
   "tool": "page_watch",
   "charge_usd": 0.005,
   "settlement_tx": "0x…"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/how-is-page-change-watcher-1b44b645/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from how.is](https://www.zero.xyz/host/how.is/llms.txt)