# AgentShelf CSS Canonical Link Extractor

> AgentShelf CSS Canonical Link Extractor is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-01).

Extracts canonical URL(s) from a public webpage or raw HTML by selecting link[rel='canonical'] elements, with SSRF protection.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/css-link-canonical?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-01
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agentshelf-css-canonical-link-extractor-33ceca06
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_daYUDci902bc1raMU-huH

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 agentshelf-css-canonical-link-extractor-33ceca06 -d '<json body>'
```

Example prompt: What's the canonical URL declared on https://example.com/some-article? Fetch the page and pull out the link[rel='canonical'] href.

## When to prefer this

Use this endpoint when you need to programmatically determine the canonical URL of a page for SEO auditing, deduplication, or crawl prioritization. Prefer the free sandbox endpoint (/v1/sandbox/css-link-canonical) for testing. Use this paid endpoint for production use where SSRF safety and reliable parsing are required. Choose this over a generic HTML fetcher when you specifically need the canonical link tag and want a clean, structured result without post-processing raw HTML yourself.

## Known failure modes

- URL is unreachable or returns non-200 status — extraction fails with an error
- SSRF-blocked URL (private IP, metadata endpoint) — rejected before fetch
- No link[rel='canonical'] element found — returns empty result
- HTML is malformed and canonical tag is unparseable — returns empty or partial result
- Input HTML exceeds 200,000 character limit — request rejected
- URL shorter than 8 characters or longer than 2048 — validation error

## How this service works

Call when an agent needs canonical hrefs via link[rel='canonical'] from a public page or HTML (SSRF-safe). Exact $0.001 USDC. Prefer unpaid POST /v1/sandbox/css-link-canonical first.

## Output

Returns the href value(s) found in link[rel='canonical'] elements from the fetched or provided HTML. Typically a single canonical URL string, or an empty result if no canonical tag is present.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "maxLength": 2048,
   "minLength": 8,
   "description": "Public page to fetch. The selector or profile is fixed by the SKU. Provide url or html."
  },
  "html": {
   "type": "string",
   "examples": [
    "<!doctype html><html lang=\"en\"><head><title>Hello</title>\n<meta charset=\"utf-8\"><meta name=\"description\" content=\"Desc\">\n<link rel=\"canonical\" href=\"https://example.com/\"><link rel=\"icon\" href=\"/favicon.ico\">\n</head><body><h1>Hello</h1><a href=\"https://example.com/a\">A</a></body></html>"
   ],
   "maxLength": 200000,
   "minLength": 1,
   "description": "HTML to extract from locally. Provide html or url. When both are set, html is used."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agentshelf-css-canonical-link-extractor-33ceca06/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agentshelf.syntexa.ch](https://www.zero.xyz/host/agentshelf.syntexa.ch/llms.txt)