HTML Validator

Analyze HTML code for open tags, nesting correctness and markup validity offline.

Processing... 0%

Analyzing markup

Tokenizing structure

Verifying nesting rules

Validating attributes

Compiling report

Result

Are you familiar with the situation when the layout of the site suddenly crawls, elements are shifted, and the reason is one forgotten closing tag `</div>` somewhere in the middle of a thousand lines of HTML code?

Our HTML validator will help you find markup errors instantly and anonymously. Because code structure analysis is performed locally in the browser, you can safely inspect even private templates or page codes.

The tool builds a tag tree, finds open structures, detects incorrect nesting, and highlights erroneous locations. The presence of mandatory attributes is additionally checked.

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Executed in Browser

Your files and inputs never leave this device. Processing runs completely offline. 100% Secure.

Accepted Formats & Rules

Validates HTML file syntax client-side with no external overhead.
Outputs a clear validation summary and statistics.
Displays a code snippet pointing to the invalid token.

Key Benefits

✓ 100% Offline: HTML files remain inside your browser for full security.

✓ Instant feedback: Highlights errors, unclosed tags, and syntax problems.

✓ Precise detection: Shows exact line numbers and error context.

Use Cases

• Do you need to quickly find the cause of a broken layout on a page?
• Do you want to check the HTML code generated by the script for compliance?
• Do you need to check the tag structure in your email template?