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HTML Validator

Short answer

Check the document basics (doctype, language, charset, viewport, title, unique IDs), obsolete HTML tags and attributes, and how iframes are embedded.

Free · No signup · Runs in your browser
100% in your browser — your content never leaves your device.

What It Does

Checks a page's HTML in three parts. Document basics: a DOCTYPE, a `lang` attribute, a charset declaration, a viewport meta tag, a `<title>` and unique `id` values. Obsolete HTML: tags such as `<center>`, `<font>` and `<marquee>`, and presentational attributes such as `align` and `bgcolor`. Embedded frames: whether each iframe has a title, loads lazily when offscreen, is sandboxed when it comes from another site and uses HTTPS. Each part lists what it found.

Why It Matters

Browsers repair broken markup silently, but assistive technology and crawlers work from whatever the parser produces. A missing `lang` or viewport tag, duplicate IDs, presentational leftovers and untitled iframes are small, fixable problems that affect accessibility, mobile rendering and how reliably the page is read.

How It Works

  1. Enter a page URL or paste its HTML

  2. We parse the raw HTML in your browser

  3. Run the document-basics, obsolete-HTML and iframe checks

  4. Return a result for each part, with the duplicate IDs, obsolete elements and iframes we found

Sample input + output
INPUT
url: https://rankproof.eu/tools
OUTPUT
Document basics                            100/100
  HTML5 doctype declared                   OK
  html lang attribute set                  OK
  character encoding declared              OK
  viewport meta present                    OK
  title element present                    OK
  no duplicate IDs                         OK

Obsolete HTML                              100/100
  no obsolete tags (center, font, …)       OK
  no obsolete attributes (align, …)        OK

Embedded frames (iframes): 2
  every iframe has a title                 warn (1 of 2)
  offscreen iframes lazy-load              OK
  third-party iframes are sandboxed        OK
  all iframes use HTTPS                    OK

2 of 3 areas look good

Who Uses This

  • Frontend Developer

    Check a preview build before merging and fix duplicate IDs or missing meta tags before they ship.

  • QA Engineer

    Add the check to your release checklist to catch markup that a CMS template change broke.

  • Accessibility Auditor

    Clear up untitled iframes, a missing lang attribute and duplicate IDs before starting a full WCAG review.

Frequently Asked Questions

Are HTML errors a ranking factor?

Not directly — Google has said valid HTML is not a ranking factor. Broken markup can still cause indirect problems, such as structured data or content that is not read the way you intended.

What counts as obsolete HTML?

Elements and attributes the HTML standard no longer supports for presentation, such as `<center>`, `<font>`, `<marquee>`, `<big>`, `<strike>`, `align`, `bgcolor` and `border`. Replace them with CSS.

Why do iframes need a title?

Screen readers announce the title so people know what a frame contains before they enter it. It is part of giving every frame an accessible name under WCAG 2.1.

Does it validate JavaScript-rendered content?

No — we check the raw HTML source, either pasted or fetched directly, not the DOM after JavaScript runs.

Does it check every HTML rule?

No — it is a fast check of the basics, obsolete markup and iframes, not a full validator for the HTML standard.

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