# x-402 Web Page Change Detector

> x-402 Web Page Change Detector is a paid API for AI agents from api.x-402.online, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-02).

Checks whether a web page's main content has changed since a previous fetch, using a SHA-256 checksum comparison.

## Facts

- Endpoint: GET https://api.x-402.online/v1/web/changed?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x-402-web-page-change-detector-93b80ad8
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_fPo8Ka_h7s8zmSYT042RJ

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 x-402-web-page-change-detector-93b80ad8
```

Example prompt: Check if the main content on https://example.com/blog/post-42 has changed since I last read it — my stored checksum from the previous fetch was a3f9c1d2e8b47560.

## When to prefer this

Choose this endpoint when you need lightweight, low-cost change detection ($0.005/call) on a specific URL without maintaining your own scraping infrastructure. It is ideal for polling loops where you already have a stored checksum from a prior call and want a simple true/false answer. Prefer this over full-scrape endpoints when you don't need the page content itself — only whether it changed. It strips navigation and boilerplate to focus on main content, reducing false positives from peripheral page updates.

## Known failure modes

- URL is unreachable or returns a non-200 status — endpoint may error or return an indeterminate result
- Page blocks bots or requires authentication — main content cannot be fetched
- Supplied checksum format is invalid — comparison may fail or be skipped
- Rate limiting or payment failure for the $0.005 USDC per-call fee — request rejected
- Dynamic pages with ads or timestamps may falsely report changed=true due to non-content elements

## How this service works

Tell whether a page changed since the last time you read it. Has a page changed since you last read it? Send a URL and the content_sha256 you kept from a previous call; get back changed: true or false, the current checksum and the current length. Without a checksum, returns the starting point. Main content only, navigat…

## Output

Returns a JSON object with: a `changed` boolean (true if the page content differs from the supplied checksum, false if identical), the `current content_sha256` checksum of the page's main content as fetched now, and the `current length` in bytes. If no prior checksum is supplied, returns the initial baseline checksum and length without a change comparison.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "properties": {}
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x-402-web-page-change-detector-93b80ad8/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.x-402.online](https://www.zero.xyz/host/api.x-402.online/llms.txt)