Validate HTML

Overview

You send HTML you already hold, inline or as a file reference. A disposable Java child runs the pinned Nu Html Checker with a fixed argument vector and returns normalized syntax diagnostics. Markup is accepted only through stdin; URL mode, schema paths, filter files and arbitrary flags are not exposed. A match against the checker is not an accessibility, rendering or live-site guarantee. A successful call costs 2 execution credits. Accepts file input via file_ref — no need to extract file content first.

HTML syntax can be checked mechanically with a pinned checker; fetching a live page would change the privacy and availability model.

When to use it

Scope

Non-goals

• Does not test accessibility
• Does not load, render or execute the document
• Does not follow links, images or other resources
• Does not fetch a URL or download a checker update

Properties

Capabilities

Cost & billing

Flat rate per invocation

File handling

File limits

Constraints this skill applies to your input and generated files. The “Limited by” column shows the static source of each cap; none of these can be raised by upgrading your plan.

How we handle your data

Input schema

Output schema

API contract

curl -sS -X POST "$BASE/v1/execute" -H "Authorization: Bearer $KEY" -H 'Content-Type: application/json' -d '{"skillKey":"web.validate_html","input":{"html":"<!DOCTYPE html><html lang=\"en\"><head><title>Hi</title></head><body><p>Hello</p></body></html>"}}'

import { Squillify } from "@squillify/sdk";

const sq = new Squillify({ apiKey: process.env.SQUILLIFY_API_KEY });

const { output } = await sq.execute("web.validate_html", {"html":"<!DOCTYPE html><html lang=\"en\"><head><title>Hi</title></head><body><p>Hello</p></body></html>"});

Errors

Other limits

Limitations

• Does not test accessibility
• Does not load, render or execute the document
• Does not follow links, images or other resources
• Does not fetch a URL or download a checker update
• Accessibility audits
• Live page fetching
• XSS cleaning, which web.sanitize_html handles

How to call

POST /v1/execute (requires authentication)

{
  "skillKey": "web.validate_html",
  "input": {
    "html": "<!DOCTYPE html><html lang=\"en\"><head><title>Hi</title></head><body><p>Hello</p></body></html>"
  }
}

Examples

{
  "html": "<!DOCTYPE html><html lang=\"en\"><head><title>Hi</title></head><body><p>Hello</p></body></html>"
}

{
  "truncated": false,
  "diagnostics": [],
  "doctype": "html",
  "title": "Hi",
  "lang": "en",
  "checkerVersion": "26.8.23 (9b5b796)",
  "documentMode": "HTML",
  "checkerCommit": "9b5b796640803ad85a3d3a9d1cb1825acf092672",
  "includeWarnings": true,
  "valid": true
}

{
  "html": "<html><p>Hi</p></html>"
}

{
  "includeWarnings": true,
  "checkerCommit": "9b5b796640803ad85a3d3a9d1cb1825acf092672",
  "truncated": false,
  "valid": false,
  "diagnostics": [
    {
      "code": "HTML_97fae2f3b03f87e1",
      "severity": "ERROR",
      "message": "Start tag seen without seeing a doctype first. Expected \"<!DOCTYPE html>\".",
      "path": "document",
      "source": "nu-html-checker",
      "location": {
        "line": 1,
        "column": 1,
        "endLine": 1,
        "endColumn": 6
      }
    },
    {
      "code": "HTML_495d1a0aad76488d",
      "severity": "WARNING",
      "message": "Consider adding a \"lang\" attribute to the \"html\" start tag to declare the language of this document.",
      "path": "document",
      "source": "nu-html-checker",
      "location": {
        "line": 1,
        "column": 1,
        "endLine": 1,
        "endColumn": 6
      }
    },
    {
      "code": "HTML_c441d85bf090bb73",
      "severity": "ERROR",
      "message": "Element \"head\" is missing a required instance of child element \"title\".",
      "path": "document",
      "source": "nu-html-checker",
      "location": {
        "line": 1,
        "column": 7,
        "endLine": 1,
        "endColumn": 9
      }
    }
  ],
  "checkerVersion": "26.8.23 (9b5b796)",
  "documentMode": "HTML"
}

Recommended use cases

• Check a saved HTML5 document for syntax errors before publishing
• Collect checker warnings on an XHTML snapshot without opening a browser

Avoid for

• Accessibility audits
• Live page fetching
• XSS cleaning, which web.sanitize_html handles

Related skills

Composable with

Safety & privacy

• Runs without calling any external service.
• Your payloads are never stored permanently.
• Telemetry captures metadata only — never your payload contents.
• We never train models on your payloads.
• No human reviews your payloads.

Tags