# Change / Diff Check

> Change / Diff Check is a paid API for AI agents from mcp.dropenginehq.com, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-01).

Compares normalized public webpage text against a previously stored SHA-256 hash to detect whether the page content has changed.

## Facts

- Endpoint: POST https://mcp.dropenginehq.com/api/check-change?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-01
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/change-diff-check-2aaa95ab
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_XajEbYxLQ7aL3XDo22uC9

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 change-diff-check-2aaa95ab -d '<json body>'
```

Example prompt: Check if the content at https://example.com/pricing has changed since I last recorded it — here's the previous SHA-256 hash: a3f1c2d9e4b7...

## When to prefer this

Use this endpoint when you need lightweight, hash-based change detection for a specific public webpage without storing full snapshots. Ideal for autonomous agents that need to cheaply verify whether a page has been modified since a prior crawl, rather than doing a full re-extract. Preferred over full-extract endpoints when you only need a yes/no change signal and already have a stored hash.

## Known failure modes

- URL is unreachable or returns non-200 status
- URL points to a non-public or paywalled page
- previous_hash is malformed or wrong length
- webpage content cannot be normalized for comparison
- rate limiting or payment failure via x402 protocol

## How this service works

Compare normalized public webpage text with a prior SHA-256 hash.

## Output

Returns whether the current normalized text of the webpage matches, differs from, or cannot be compared to the provided SHA-256 hash — likely including a changed/unchanged status flag and potentially the new hash of the current page content.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "format": "uri",
   "maxLength": 4096
  },
  "previous_hash": {
   "type": "string",
   "maxLength": 80,
   "minLength": 1
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/change-diff-check-2aaa95ab/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from mcp.dropenginehq.com](https://www.zero.xyz/host/mcp.dropenginehq.com/llms.txt)