# Webwache Canonical Change Snapshot

> Webwache Canonical Change Snapshot is a paid API for AI agents from webwache.halowerk.com, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-22).

Fetches a passive public snapshot of a target URL and evaluates a documented change criterion, returning an observation, verdict, evidence source, and limitations.

## Facts

- Endpoint: POST https://webwache.halowerk.com/v1/canonical-change-snapshot?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-22
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/webwache-canonical-change-snapshot-eeca7597
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_mUyOdNh9apKpdv9MMj7Li

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-snapshot-eeca7597 -d '<json body>'
```

Example prompt: Take a passive snapshot of https://example.com and check whether the page content has changed compared to the baseline I stored last week — give me the observation, verdict, and the exact evidence source you used.

## When to prefer this

Choose this endpoint when you need a passive, non-intrusive point-in-time snapshot of a public webpage to evaluate a specific observable criterion — especially when you want structured verdict output (observation + threshold + evidence source) rather than raw HTML. Prefer this over general web scrapers when you need built-in change comparison via a baseline parameter and an explicit pass/fail verdict. Not appropriate when login, form submission, or dynamic interaction with the page is required.

## Known failure modes

- Target URL is unreachable or returns non-200 status — snapshot cannot be completed
- Target requires authentication or is behind a paywall — passive read is blocked
- Content is JavaScript-rendered and not accessible in static fetch — observation may be incomplete
- Rate limiting or bot protection on target blocks the fetch
- Baseline object is malformed or from an incompatible schema version — comparison fails
- Target domain normalizes incorrectly from bare domain input

## How this service works

Canonical change snapshot 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

Returns a structured object containing: the observation (what was found on the page), a threshold or criterion evaluation, a verdict (pass/fail/uncertain), the exact evidence source URL, any limitations on the passive read, and a mode-specific recommended action. The baseline object can be stored and passed back on subsequent calls for comparison.

## 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-snapshot-eeca7597/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)