# Webwache Canonical Change Compare

> Webwache Canonical Change Compare is a paid API for AI agents from webwache.halowerk.com, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-21).

Passively fetches a target URL and compares its current public content against a baseline or comparison URL to detect and evaluate changes against a specified criterion.

## Facts

- Endpoint: POST https://webwache.halowerk.com/v1/canonical-change-compare?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-21
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/webwache-canonical-change-compare-a4e588a1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_YdboRabbEBKPVkHOuD945

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 webwache-canonical-change-compare-a4e588a1 -d '<json body>'
```

Example prompt: Check if the pricing page at stripe.com/pricing has changed compared to this baseline snapshot I saved last week, and tell me your verdict along with the exact evidence you found.

## When to prefer this

Use this endpoint when you need a passive, read-only comparison of a public web resource against a baseline or a second URL to detect changes or evaluate a criterion. Prefer it over generic scraping tools when you need a structured verdict with evidence provenance and limitation disclosure. It is ideal for monitoring workflows where you already have a baseline snapshot and want to evaluate drift without triggering any active interaction with the target site.

## Known failure modes

- Target URL is unreachable or returns non-200 status — endpoint may return an error or limited observation
- Target requires authentication — passive fetch will fail or return login page content instead of actual content
- Target blocks crawlers via robots.txt or rate limiting — observation may be incomplete or empty
- Baseline schema mismatch — if the supplied baseline is from an incompatible snapshot version, comparison may be undefined
- Comparison URL is unavailable — verdict may fall back to single-source analysis only
- Very large pages may be truncated, affecting completeness of the evidence

## How this service works

Canonical change comparison fetches current public evidence from the supplied target and evaluates the documented criterion. It returns the observation, threshold, verdict, exact evidence source, limitations and a mode-specific action. The check is passive: no login attempt, payload injection, exploit, purchase, form submission or load test is performed.

## Output

The endpoint returns an observation describing what was found on the target, a threshold evaluation, a pass/fail verdict, the exact evidence source URL used, any limitations of the passive check, and a mode-specific recommended action. No login, form submission, or active probing is performed.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "target": {
   "type": "string",
   "maxLength": 2048,
   "minLength": 3,
   "description": "Public HTTP(S) URL or domain to inspect. A bare domain is normalized to HTTPS."
  },
  "context": {
   "type": "object",
   "description": "Optional non-secret correlation labels returned unchanged only in the request lifecycle.",
   "maxProperties": 12,
   "additionalProperties": {
    "type": [
     "string",
     "number",
     "boolean",
     "null"
    ]
   }
  },
  "baseline": {
   "type": [
    "object",
    "null"
   ],
   "description": "Optional baseline returned by a previous snapshot call.",
   "additionalProperties": true
  },
  "compare_url": {
   "type": "string",
   "maxLength": 2048,
   "minLength": 3,
   "description": "Optional public comparison URL. Used by change and monitoring services."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/webwache-canonical-change-compare-a4e588a1/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from webwache.halowerk.com](https://www.zero.xyz/host/webwache.halowerk.com/llms.txt)