# HTML Validator

https://rankproof.eu/tools/seo-html-validation

## Short answer

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

## 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.

## 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

```text
url: https://rankproof.eu/tools
```

OUTPUT

```text
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
```

## 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.

## 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.

## Related Tools in SEO Analysis

- [Title & Meta Description Checker](https://rankproof.eu/tools/seo-meta-title)
- [Heading Tag Checker](https://rankproof.eu/tools/seo-heading-tags)
- [Image Alt Text Checker](https://rankproof.eu/tools/seo-image-alt)
- [Canonical URL Checker](https://rankproof.eu/tools/seo-canonical-url)
- [Robots.txt Analyzer](https://rankproof.eu/tools/seo-robots-txt)
- [robots.txt Generator](https://rankproof.eu/tools/seo-robots-txt-generator)