# Canonical URL Declarations — Attribute Presence Check

> Canonical URL Declarations — Attribute Presence Check is a paid API for AI agents from market.datapackvibe.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-21).

Checks whether a specific attribute (and optionally its value) is present on canonical URL link elements in a given webpage or HTML snippet.

## Facts

- Endpoint: POST https://market.datapackvibe.com/x402/assistant-bx-web-canonical-attribute-presence?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-21
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/canonical-url-declarations-attribute-presence-check-e596567d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_rLs4yIzzkW5DVae4gRR6_

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-attribute-presence-check-e596567d -d '<json body>'
```

Example prompt: Check if the canonical link tag on https://example.com/blog/post-1 has an attribute called 'id' with the value 'canonical-main' — use static HTML parsing, no JavaScript rendering needed.

## When to prefer this

Choose this endpoint when you need a lightweight, static check for the presence of a specific HTML attribute on a canonical link tag — particularly useful for SEO audits, CI/CD validation pipelines, or monitoring canonical tag markup compliance without needing full browser rendering or JavaScript execution. Ideal when cost efficiency matters ($0.01 per call) and the target page is publicly accessible over HTTPS.

## Known failure modes

- URL is not publicly accessible or returns non-200 status
- HTML content exceeds 100,000 character limit
- Attribute name does not match required pattern (must start with letter, alphanumeric/colon/underscore/hyphen)
- No canonical link element found in the page
- Supplied URL and HTML both empty or malformed
- Term parameter missing or empty (minLength 1 required)

## How this service works

Canonical URL declarations — Attribute presence check: Attribute presence check 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 attribute presence check result.

## Output

Returns a bounded attribute presence check result indicating whether the specified attribute (and optionally its expected value) exists on the canonical URL link element found in the parsed page or HTML snippet. No JavaScript rendering is performed; the check is based on static HTML parsing only.

## 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-attribute-presence-check-e596567d/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)