What is the difference between HTML4 and HTML5 validation?

HTML5 validation checks for correct use of new semantic elements, removed deprecated elements, and updated attribute rules. HTML4 validation uses an older, stricter DTD-based specification.

Which doctype should I use for HTML5?

Use ` ` — it is the standard HTML5 doctype. It tells browsers and validators to use the HTML5 parsing rules, which are more lenient than the strict XHTML rules of earlier standards.

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Validate HTML5 Online

HTML5 introduced new elements, removed old ones, and changed attribute requirements. FixTools validates your HTML5 code against the current specification, catching deprecated patterns and incorrect HTML5 usage before they cause problems.

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Validates against the HTML5 specification

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Flags deprecated HTML4 patterns

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Checks new HTML5 element usage

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How to use this tool

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Paste your HTML5 code and validate. The tool checks for correct use of HTML5 elements, attributes, and patterns.

How It Works

Step-by-step guide to validate html5 online:

1
Add the HTML5 doctype
Confirm your HTML starts with <!DOCTYPE html> before validating.
2
Paste your HTML5
Paste the complete HTML5 document or component.
3
Validate
Click Validate to check against the HTML5 specification.
4
Fix deprecated patterns
Replace any flagged deprecated HTML4 elements or attributes with their HTML5 equivalents.

Real-world examples

Common situations where this approach makes a real difference:

Migrating an HTML4 site to HTML5

Run every page through the HTML5 validator to identify deprecated elements, font and table layout patterns, and missing HTML5 doctype declarations.

Ensuring a new project is HTML5-compliant

For new projects targeting modern browsers, validate all HTML5 code to confirm correct use of new semantic elements and attribute syntax.

When to use this guide

Use this when migrating legacy HTML to HTML5 or when building HTML5-first projects that need to avoid deprecated elements and patterns.

Pro tips

Get better results with these expert suggestions:

Always declare the HTML5 doctype

Every HTML5 document must start with <!DOCTYPE html>. Without it, browsers enter quirks mode and may render your page differently from modern standards.

Replace deprecated elements

HTML5 removed elements like <font>, <center>, <marquee>, and <frame>. Validation will flag these — replace them with CSS equivalents.

Use semantic HTML5 elements

HTML5 introduced <header>, <nav>, <main>, <article>, <section>, <aside>, and <footer>. Use these instead of <div> where semantically appropriate.