Website Tools

HTML Validator

Check a webpage's HTML for structural errors, missing tags, and accessibility issues.

Enter a URL below to check its HTML for structural errors, missing tags, and common accessibility issues.

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JustChecker tracks your website's health continuously, catching problems before they affect your visitors.

What Is the HTML Validator?

It fetches a page and checks its HTML for common problems: parse errors, a missing or unusual DOCTYPE, a missing lang attribute, duplicate id values, images without alt text and a missing <title>.

When to Use It

When a layout breaks in one browser but not another.
As a quick accessibility and SEO hygiene check.
After changing templates or themes.

How to Use It

Enter the page URL.
Review errors first, then warnings.

Understanding the Result

Duplicate IDs break scripts and labels. Missing alt text hurts screen-reader users and image search. A missing lang attribute makes it harder for browsers and assistive technology to handle the page's language.

Limitations

It checks the HTML delivered by the server, not content added later by JavaScript, and it is not a full W3C specification validator - use validator.w3.org for exhaustive checks. Check stylesheets with the CSS Validator.

Frequently Asked Questions

It parses the page's HTML and reports real structural parsing errors, plus checks for a missing DOCTYPE, a missing lang attribute, duplicate id attributes, images missing alt text, and a missing title tag.

No - this is a lightweight validator focused on the most common, impactful issues. For a full specification-level validation report, the official W3C Markup Validator is more exhaustive.

HTML ids must be unique on a page. Duplicates can break CSS targeting, JavaScript that uses getElementById, in-page anchor links, and accessibility tools that rely on unique ids.