Developer ToolsCode ValidatorsFree Tool
HTML Validator
Validate HTML5 markup for errors, accessibility issues, and best-practice warnings — instantly in your browser.
How to Use HTML Validator
- 1Paste your full HTML document or a snippet into the 'HTML Code' text area. The placeholder shows a minimal valid HTML5 document as a reference.
- 2Click the Validate button. The tool parses your HTML and checks it against HTML5 rules and best practices.
- 3Review the results summary: Errors (✕ red) are spec violations that must be fixed; Warnings (⚠ amber) are best-practice issues; Suggestions (ℹ blue) are optional improvements.
- 4Read each issue message — it explains exactly what is wrong, which element is affected, and how to fix it (e.g. 'add alt="" to decorative images').
- 5Fix the issues in your code, paste the corrected HTML back in, and click Validate again to confirm all issues are resolved.
- 6Click the reset button (↺) to clear the editor and start fresh with new HTML.
Frequently Asked Questions
It checks for missing required elements (DOCTYPE, title, charset, viewport meta), images without alt text, deprecated tags (font, center, marquee, etc.), unlabelled form inputs, empty or href-less anchors, multiple <h1> elements, skipped heading levels, and render-blocking scripts in <head>.
Errors (✕) are violations of the HTML5 spec that will cause broken or inaccessible pages and must be fixed. Warnings (⚠) are best-practice issues that won't break the page but affect SEO, accessibility, or maintainability. Suggestions (ℹ) are performance or style tips that are optional but recommended.
No. This tool runs entirely in your browser using the built-in HTML parser, so it gives instant results without sending data to a server. The W3C validator at validator.w3.org applies the full HTML5 specification — for production code, both are worth using.
Yes. Paste any fragment of HTML and click Validate. Checks that require a full document (like DOCTYPE or <title>) will show a warning, but snippet-level issues like missing alt attributes or deprecated tags will still be reported correctly.
Completely. All validation runs in your browser using the built-in DOMParser API. No code is sent to any server.
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