Checks well-formedness (balanced, properly-nested tags) in your browser — not full HTML5 spec conformance. Nothing is uploaded.
Validate HTML syntax online, free. HTML is the markup language that structures content on the web. This validator checks your HTML against WHATWG HTML Standard and reports syntax errors with clear messages — processing runs in your browser with nothing uploaded.
It parses your HTML and pinpoints syntax errors so you can fix them before they break a build or deploy. 100% free, no registration, and complete privacy — everything runs locally in your browser, so your data never touches a server.
Find HTML syntax problems instantly, with messages that point to what needs fixing.
Validation follows WHATWG HTML Standard, so a pass means standards-compliant HTML.
Your HTML is parsed locally in JavaScript; nothing is uploaded, logged, or stored.
Unlimited validation with no account or quota, on desktop and mobile.
Paste your HTML into the input box and click Validate. The validator runs instantly in your browser and shows the result on the right — no upload, no signup, no installation.
Yes. The HTML validator is completely free with no limits, no account, and no watermark. All processing happens locally in your browser for privacy.
No. Your HTML never leaves your device — it is processed locally in JavaScript. We don't upload, log, or store your input, so it's safe for proprietary code and config.
It checks your HTML for syntax errors and structural validity against WHATWG HTML Standard, and reports clear messages pointing to anything that needs fixing.
Yes. The tool is fully responsive and works on phones, tablets, and desktops — just open it in any modern browser.