HTML Validator — W3C-style HTML Linting & Formatting

Validate your HTML structure and formatting instantly. This tool checks for common errors, accessibility issues, and formatting mistakes using W3C-style rules — in-browser and private.

HTML Validator (W3C-style)
Paste your HTML code
Some HTML rules are invalid. See the errors below.
1
<div>hello</div><img src>

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Instant HTML Validation

Paste your HTML and instantly see any issues with 700ms debounce. Errors appear line-by-line with full context. Fix problems and re-validate — all without needing a backend server.

Key Features

  • ⚙️ Optional auto-format before validation
  • 📄 Toggle: Full HTML document or snippet mode
  • 🪄 700ms debounce input handling
  • 🔍 Highlights all error lines inline
  • 🔐 Private — no data sent or stored

Why Validate Your HTML?

  • 🔍 Improve accessibility with proper alt and semantic tags
  • 🧩 Catch structural bugs in components or templates
  • 📄 Clean up exported HTML from visual tools
  • 📈 Improve SEO with valid, clean markup
  • ⚡ Ensure consistent rendering across browsers

Rules Checked (Sample)

  • ❌ Missing or duplicate id attributes
  • ❌ Empty src values
  • ❌ Missing alt text on images
  • ❌ Improper tag casing like <Div>
  • ❌ Tag pairs not closed properly
  • ❌ Missing DOCTYPE (when validating full document)
  • ❌ Inline style usage

Who Should Use This Tool?

  • 👩‍💻 Web developers writing raw HTML
  • 📬 Email template creators
  • 🎨 Designers exporting HTML from no-code tools
  • 🧪 QA testers validating frontend output
  • 📘 HTML students learning best practices

How to Use

  1. Paste or type your HTML into the editor
  2. Enable/disable “Auto Format” and “Validate as Document”
  3. Wait 700ms for live validation to trigger
  4. Review any inline errors or copy the formatted output

Why ToolMateX HTML Validator?

  • 🚀 Fast & fully browser-based
  • 📐 Auto-format toggle built-in
  • 💡 Helpful error explanations per line
  • 🔒 100% privacy — no uploads, no logs
  • 🆓 Free to use forever

Frequently Asked Questions (FAQs)

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Tired of bloated tool websites with 10 ads per click? This platform is built for speed, simplicity, and reliability. Whether you're debugging JSON or testing colors, we’ve got your back.

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