HTML Formatter
Beautify and indent HTML markup.
OpenValidate HTML markup. - runs entirely in your browser. Free, fast and private.
Load a page fragment or full document to inspect.
Unclosed tags, nesting problems, and attribute errors are checked.
Each issue shows line context and a plain-English explanation.
Edit the source and rerun until the markup passes checks.
HTML Validator is a free code utility on OneDevToolkit. Validate HTML markup. It runs in your browser for this session - use the workspace on this page to try it.
Need a related step? Open the Code Tools hub at /code-tools/ or the <a href="/blog/">blog</a> for longer workflows.
Processes data instantly with no server round-trips.
Your data never leaves your browser. Nothing is uploaded.
Works in any modern browser. Nothing to download or install.
No limits, no sign-up, no credit card required.
Works on desktop, tablet and mobile devices.
Beautiful in both themes. Your preference is saved.
Keyboard shortcut
Use HTML Validator to format, validate, or transform data while debugging or reviewing a PR.
Keep payloads on your device - no upload farm between you and the result.
Chain related code tools in Recipe Studio when you need multi-step transforms.
Answers for this tool. For site-wide help, open the FAQ hub.
HTML Validator Validate HTML markup. It runs entirely in your browser with instant feedback.
No server upload is required for formatting/validation. Clearing the page removes the text from memory.
Validators report problems; formatters beautify valid structure. Severely broken input may need manual fixes first.
Formatters and converters aim to preserve meaning. Always review diffs for mission-critical code before committing.
Paste smaller chunks if the tab slows down. Minifiers and deep validators scale with input size on the CPU you have.
Many tools support Ctrl/⌘+Enter to run and standard copy shortcuts. Check the tool toolbar for Sample / Clear / Download.
When options exist (spaces vs tabs, indent width), set them before copying output into your repo to match project style.
After the page loads, formatting continues offline. CDN libraries need an initial network load.
Bookmark HTML Validator, copy output into editors, or chain steps with Recipes.