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ValidateHTML

Free HTML5 Validator

Check your HTML5 code against the latest web standards. Catch deprecated elements, missing attributes, and specification violations instantly.

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Ctrl+Enter to validate

What Does an HTML5 Validator Check?

HTML5 introduced significant changes to the web standard, including new semantic elements like <article>, <section>, <nav>, and <header>. At the same time, many older elements were deprecated.

Our HTML5 validator checks for deprecated elements like <center>, <font>, <marquee>, and <blink>. It also verifies that required attributes are present, like alt on images and proper DOCTYPE declarations.

Common HTML5 Issues

Missing DOCTYPE

HTML5 requires <!DOCTYPE html> at the top of every document.

Deprecated Elements

Tags like <center>, <font>, and <big> are no longer valid in HTML5.

Missing Alt Attributes

Images must have alt text for accessibility and HTML5 compliance.

Incorrect Nesting

Block elements inside inline elements violate HTML5 content models.

Missing Lang Attribute

The <html> element should have a lang attribute for accessibility.

Unclosed Tags

While HTML5 is more lenient, unclosed tags can cause unpredictable rendering.