# HTML Canonical Link Check

> HTML Canonical Link Check is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Compares and validates a document URL against its canonical URL using deterministic normalization, returning a pass or advisory status.

## Facts

- Endpoint: POST https://api.delx.ai/api/v1/x402/html-canonical-link-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/html-canonical-link-check-4fc6601d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_78b9P-iMfH6bGlvyPkKzs

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 html-canonical-link-check-4fc6601d -d '<json body>'
```

Example prompt: Check whether 'https://example.com/blog/post?utm_source=twitter' and its canonical URL 'https://example.com/blog/post' are consistent — normalize both and tell me if they pass or if there's an advisory.

## When to prefer this

Use this endpoint when you need a lightweight, deterministic, no-external-dependency check to verify that a page's canonical link tag matches its document URL — particularly useful in web scraping pipelines, SEO audits, caching layers, or redirect chains where canonical mismatches should be flagged before proceeding. Prefer this over full HTML parsing services when you only need URL-level canonical equivalence without broader content analysis.

## Known failure modes

- Malformed or non-URL input strings may cause validation errors
- URLs exceeding 8192 characters will be rejected
- Relative URLs without a base may not normalize correctly
- Network or upstream server errors returning non-2xx status
- Edge cases in URL normalization (e.g. unicode, encoding differences) may produce unexpected advisory results

## How this service works

Html Canonical Link Check: Html Canonical Link Check compares document and canonical URLs after deterministic normalization from bounded caller-supplied values without an external provider. Call Html Canonical Link Check before accepting, caching, redirecting, or retrying a caller-supplied web response. Returns normalized web evidence, the computed finding, and an explicit pass or advisory status for Html Canonical Link Check as versioned deterministic JSON. Price: $0.001 USDC via x402 on Base.…

## Output

A versioned deterministic JSON object containing the normalized document URL, the normalized canonical URL, the computed match finding, and an explicit pass or advisory status indicating whether the two URLs are canonically equivalent.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "document_url": {
   "type": "string",
   "maxLength": 8192,
   "description": "Document URL supplied to Html Canonical Link Check; used only for this bounded calculation and processed in memory without retention."
  },
  "canonical_url": {
   "type": "string",
   "maxLength": 8192,
   "description": "Canonical URL supplied to Html Canonical Link Check; used only for this bounded calculation and processed in memory without retention."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "result": {
   "left": "https://example.com/page",
   "right": "https://example.com/page",
   "matched": true
  },
  "schema": "delx/util-html-canonical-link-check/v1",
  "status": "pass",
  "evidence": {
   "retained": false,
   "input_sha256": "592c02dfd1b6df477a94ca4c931b3a3f08c24e00f6ccaf91931c0bf89268d170",
   "external_calls": 0
  },
  "operation": "web_reliability:html_canonical_link_check"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/html-canonical-link-check-4fc6601d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.delx.ai](https://www.zero.xyz/host/api.delx.ai/llms.txt)