HTML5 Validator
Check HTML code for common errors and HTML5 standard compliance.
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About HTML5 Validator
Check HTML code for common errors and HTML5 standard compliance.
HTML5 Validator reviews your markup against the HTML5 standard and points out what needs fixing. It detects missing doctypes, unclosed or wrongly nested tags, deprecated elements, duplicate ids, invalid attribute values, broken alt text on images and structural mistakes like skipping main landmarks. Errors are listed with their line numbers and plain-English explanations, while warnings highlight practices that work today but may cause trouble later. Paste a full page or a fragment — the validator fills in context automatically — and re-check after each edit until the report comes back clean. Front-end developers use it before shipping, students use it for assignments and marketers use it to clean landing page code. HTML5 Validator is free, runs in your browser and keeps your source private.
How to Use HTML5 Validator
- Paste your code, markup or configuration into the editor.
- Choose the output format or options offered.
- The formatted result updates live.
- Copy or download the finished code.
Key Features
- Clean, consistently formatted output ready to paste.
- Supports the common formats used in web development.
- One-click copy and download — no build step required.
Frequently Asked Questions
What common errors does the HTML5 Validator find?
Missing or wrong doctypes, unclosed tags, incorrect nesting, deprecated elements, duplicate ids, invalid attributes, missing alt text and broken form labels are the most frequent catches. Every error comes with a line number and a short fix, so you can clean the page in one pass.
Is HTML5 Validator free to use?
Yes. HTML5 Validator is completely free with unlimited use — no account, download or payment required.
Is my data uploaded to a server?
No. HTML5 Validator runs entirely in your browser. Your inputs are never sent to our servers or stored anywhere.
Does HTML5 Validator work on mobile?
Yes. The interface is fully responsive and works in any modern browser on Android, iPhone, tablets and desktops.
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