HTML Validator
Check HTML tag closing and nesting, and locate common structural problems.
What is an HTML validator?
An HTML validator is an online checker for finding structural problems in web markup. It checks the DOCTYPE, html root, tag closing, nesting, duplicate attributes, duplicate ids, and common details such as image alt, link href, and html lang. Line and column positions help you clean snippets, investigate rendering problems, and improve basic accessibility.
How to use the online HTML validator
- Paste a complete HTML document or the snippet you want to inspect. You can load the example first to see the result format.
- Click Validate HTML. Fix errors first, then review warnings for semantic and accessibility improvements. Errors usually require structural correction, while warnings need judgment.
- Use the reported line and column to return to the source. Check missing closing marks, duplicate attributes, or incorrect nesting, then validate again after editing.
- Copy the validation report, or continue with the HTML formatter, semantic checker, and a real browser after correcting the source.
What does the HTML validator check?
Document skeleton
Checks the HTML5 DOCTYPE, html root, and lang attribute to help establish a stable document entry point.
Tag structure
Finds orphan closing tags, incorrect closing order, and unclosed tags that often cause unexpected page structure.
Attributes and accessibility hints
Flags duplicate attributes and ids, plus basic issues such as img without alt and a without href, providing a starting point for semantic improvements.
Fast local checking
The source is analyzed in the current browser, making the tool useful for snippets, email templates, landing-page drafts, and learning examples without deploying a file first.
HTML validation frequently asked questions
Does it automatically fix HTML?
No. The validator reports findings and positions while keeping your original source unchanged. Edit the markup yourself and validate again.
Why can a browser display it while the validator reports errors?
Browsers often recover from malformed markup and may still render a page, but browsers, assistive technologies, and future maintenance can behave differently. Validation makes the intended structure explicit instead of relying on browser recovery.
Does this replace a complete standards validator?
No. This is a fast browser-side checker for common tag and attribute issues. It does not implement every WHATWG rule and does not validate CSS, JavaScript runtime behavior, server headers, or remote resources. Use project tests and a full standards validator for formal release review.
Is my source uploaded to a server?
Validation runs in the current browser, and the tool does not actively upload source for this check. For confidential code, follow your security policy and review external resources you add.
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HTML Semantic Checker
Check heading structure, image alt text, form labels, lang attributes, and semantic HTML basics.
HTML Formatter
Format HTML tags, indentation, and line breaks to make minified or messy code easier to read.
HTML Cleaner
Clean unnecessary styles, empty tags, inline attributes, and editor-generated HTML code.