# fetchwerk Diff — Content Change Detection

> fetchwerk Diff — Content Change Detection is a paid API for AI agents from fetch.halowerk.com, paid per call via x402, $0.003/call, status unknown (last checked 2026-09-14).

Compares a web page against its last stored snapshot, or two supplied documents, and returns only the content that has changed.

## Facts

- Endpoint: POST https://fetch.halowerk.com/diff
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fetchwerk-diff-content-change-detection-17a2842a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_BQsLLKiNRIxq9K6Nr3ErV

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 fetchwerk-diff-content-change-detection-17a2842a -d '<json body>'
```

Example prompt: Can you check what's changed on https://example.com/pricing since yesterday — compare the current version against its last stored snapshot and just show me what's different?

## When to prefer this

Choose this endpoint when you need to detect what specifically changed on a page or between two documents — not just whether a change occurred. It is ideal for monitoring tasks (pricing pages, regulatory filings, news articles) where you want a precise delta rather than a full re-extraction. If you have two documents in hand and want an offline comparison without any network access, supply before and after directly. Prefer a full-extraction sibling endpoint if you need the complete current content rather than just the delta.

## Known failure modes

- URL not yet stored in the system (no prior snapshot available to compare against)
- Invalid or unreachable URL returns a fetch error
- Malformed HTML or Markdown in before/after fields causes parsing failure
- 'since' timestamp predates any stored snapshot, returning no baseline
- Both url and before/after fields omitted, leaving the comparison target ambiguous
- Rate limiting or payment failure (x402 protocol) blocks the call

## How this service works

Compare a page against its last stored state, or two supplied documents, and report only the content changes.

## Output

A structured diff report highlighting only the content that changed between two document versions — removed text, added text, and modified sections — along with optional echoed timestamps for provenance tracking.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "format": "uri",
   "description": "Page to fetch and compare against its last stored state."
  },
  "after": {
   "type": "string",
   "description": "Later document as HTML or Markdown."
  },
  "since": {
   "type": "string",
   "format": "date-time",
   "description": "ISO timestamp. Picks the stored state at or before this moment instead of the newest one."
  },
  "before": {
   "type": "string",
   "description": "Earlier document as HTML or Markdown. No network access is used."
  },
  "after_fetched_at": {
   "type": "string",
   "format": "date-time",
   "description": "Optional, echoed back for inline comparisons."
  },
  "before_fetched_at": {
   "type": "string",
   "format": "date-time",
   "description": "Optional, echoed back for inline comparisons."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fetchwerk-diff-content-change-detection-17a2842a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from fetch.halowerk.com](https://www.zero.xyz/host/fetch.halowerk.com/llms.txt)