# Canonical URL Invisible Character Flags Detector

> Canonical URL Invisible Character Flags Detector 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).

Scans a web page or HTML snippet for invisible/unusual Unicode characters within canonical URL declarations and flags any anomalies found.

## Facts

- Endpoint: POST https://market.datapackvibe.com/x402/assistant-bx-web-canonical-unicode?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-invisible-character-flags-detector-57dc7a17
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_q7CyldQn5-HzaaYNr5ZX6

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-invisible-character-flags-detector-57dc7a17 -d '<json body>'
```

Example prompt: Check this page's canonical URL tag for any invisible or hidden Unicode characters — use the HTML I'm pasting here: <!doctype html><html><head><link rel="canonical" href="https://example.com/page" id="canonical-tag"></head><body></body></html> and look at the element with id 'canonical-tag'.

## When to prefer this

Choose this endpoint when you specifically need to detect invisible or non-printing Unicode characters embedded in HTML canonical URL declarations, such as for SEO integrity audits, security reviews of canonical tag manipulation, or QA pipelines validating page metadata before publication. It is not a general HTML parser or full SEO auditor — it is a specialized invisible-character detector scoped to canonical link elements.

## Known failure modes

- URL is unreachable or returns non-200 status — parsing falls back to empty or error result
- HTML exceeds 100,000 character limit — input rejected
- No canonical link element found in the document — empty flags result returned
- JavaScript-rendered canonical tags not detected — only static HTML is parsed
- Malformed HTML may cause incomplete parsing results

## How this service works

Canonical URL declarations — Invisible character flags: Invisible character flags 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 invisible character flags result.

## Output

Returns a bounded result flagging any invisible or unusual Unicode characters found within canonical URL declarations in the provided HTML or fetched page, including details about the flagged characters and their positions within the canonical element.

## 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-invisible-character-flags-detector-57dc7a17/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)