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ValidateHTML

Validate Your HTML Instantly

Paste your HTML code or enter a URL to check for errors, warnings, and best practices. Get a quality score with detailed reports.

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Ctrl+Enter to validate
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Instant Validation

Get results in milliseconds. No waiting, no page reloads. Just paste and validate.

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Quality Score

Get a 0-100 score and letter grade for your HTML quality. Track your improvements over time.

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URL Validation

Enter any URL and we'll fetch and validate the HTML for you. Check any live website.

How It Works

1

Paste or Enter URL

Paste your HTML code directly or enter a URL to validate.

2

Click Validate

Our engine checks against HTML standards and best practices.

3

Fix Issues

Review errors and warnings with line numbers and rule explanations.

Why Validate Your HTML?

Valid HTML ensures your website renders correctly across all browsers and devices. Invalid markup can cause layout issues, accessibility problems, and hurt your SEO rankings.

Search engines like Google prefer well-structured HTML. Clean, valid code improves crawlability and helps search engines understand your content better, leading to better rankings.

ValidateHTML checks your code against modern HTML5 standards and best practices, catching common mistakes like missing alt attributes, unclosed tags, deprecated elements, incorrect nesting, and more.

Frequently Asked Questions

What HTML errors does ValidateHTML check for?▼
ValidateHTML checks for a wide range of HTML issues including: unclosed tags, missing required attributes (like alt on images), deprecated HTML elements (like center, font), incorrect tag nesting, missing DOCTYPE declaration, invalid attribute values, accessibility issues, and more. We follow the latest HTML5 specification and web best practices.
Is ValidateHTML free to use?▼
Yes, ValidateHTML is completely free. You can validate unlimited HTML code snippets and URLs at no cost. No registration required.
How is the HTML quality score calculated?▼
Your HTML quality score starts at 100 and is reduced based on the issues found. Each error deducts 10 points and each warning deducts 3 points. A score of 90-100 gets an A grade, 75-89 gets a B, 50-74 gets a C, 25-49 gets a D, and below 25 gets an F.
What is the difference between HTML errors and warnings?▼
Errors are violations of the HTML specification that can cause rendering problems, accessibility issues, or broken functionality. Warnings are best practice recommendations that won't break your page but could improve code quality, maintainability, and SEO.
Does HTML validation affect SEO?▼
Yes. While Google doesn't directly penalize invalid HTML, clean markup improves crawlability, reduces rendering errors, and ensures search engines can properly parse your content. Valid HTML also improves accessibility, which is increasingly important for SEO.