# Canonical URL Declarations — Prior Text-Set Comparison

> Canonical URL Declarations — Prior Text-Set Comparison is a paid API for AI agents from market.datapackvibe.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-13).

Parses a web page's canonical URL link element and compares its text or attribute value against a set of previously known strings to detect changes.

## Facts

- Endpoint: POST https://market.datapackvibe.com/x402/assistant-bx-web-canonical-compare?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/canonical-url-declarations-prior-text-set-comparison-03169d96
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_0Jmt7XRxIfe__hX2FsVgd

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 canonical-url-declarations-prior-text-set-comparison-03169d96 -d '<json body>'
```

Example prompt: Check whether the canonical URL on https://example.com/product-page has changed — compare it against these previously seen values: ['https://example.com/product-page', 'https://example.com/old-product'] using the href attribute of the element with id 'canonical-tag'.

## When to prefer this

Choose this endpoint when you need a lightweight, low-cost static parse of a page's canonical URL declaration and want to compare it against a known set of prior values to detect drift or confirm stability. Ideal for SEO monitoring pipelines, CMS migration audits, and agentic workflows that need to track canonical URL changes over time without requiring JavaScript rendering or login access.

## Known failure modes

- URL is inaccessible or returns non-200 status — parsing fails with an error
- HTML does not contain a canonical link element — empty or null result returned
- JavaScript-rendered canonical tags are not detected — static parsing only, no JS execution
- Attribute or attribute_value selector finds no matching element — comparison cannot proceed
- HTML input exceeds 100,000 character limit — request rejected
- previous_texts array exceeds 200 items — request rejected

## How this service works

Canonical URL declarations — Prior text-set comparison: Prior text-set comparison for Canonical URL declarations. One public HTTPS page or supplied HTML; static parsing, no JavaScript rendering, login or access bypass. Specialised preset in a shared 50-profile, 20-operation engine. 0.01 USDC includes one bounded prior text-set comparison result.

## Output

Returns a bounded comparison result indicating whether the canonical URL element's extracted text or attribute value matches, partially matches, or differs from the provided set of previously known strings, along with the extracted current value.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "default": "",
   "maxLength": 2048
  },
  "html": {
   "type": "string",
   "default": "<!doctype html><html><head></head><body><link rel=\"canonical\" href=\"https://www.iana.org/help/example-domains\" id=\"sample\"></body></html>",
   "maxLength": 100000
  },
  "term": {
   "type": "string",
   "default": "product",
   "maxLength": 100,
   "minLength": 1
  },
  "attribute": {
   "type": "string",
   "default": "id",
   "pattern": "^[a-zA-Z][a-zA-Z0-9:_-]{0,49}$",
   "maxLength": 50
  },
  "previous_texts": {
   "type": "array",
   "items": {
    "type": "string",
    "default": "",
    "maxLength": 1000
   },
   "default": [
    "Older example"
   ],
   "maxItems": 200,
   "minItems": 0
  },
  "attribute_value": {
   "type": "string",
   "default": "sample",
   "maxLength": 200
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/canonical-url-declarations-prior-text-set-comparison-03169d96/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from market.datapackvibe.com](https://www.zero.xyz/host/market.datapackvibe.com/llms.txt)