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HTML Formatter & Validator — Beautify, Preview & Audit HTML Online

Format · Minify · Validate · Live Preview · JSX · React · Vue · Accessibility · SEO · Security

📂 Import File or drag & drop .html / .jsx / .vue file anywhere

Ctrl+M to cycle

INPUT

INDENT

Remove CommentsSort Attrs A–ZWrap Attrs

In: 0 chars ·0 lines ·0 B

OUTPUT

</>

Output appears here

Paste HTML on the left · click a Sample · or drop a .html file

Waiting for input…

Ctrl+Enter FormatCtrl+M ModeCtrl+Shift+C CopyCtrl+L ClearCtrl+S DownloadV PreviewP Pin

What is an HTML Formatter?

An HTML Formatter beautifies raw, minified, or messy HTML code into properly indented, human-readable format. CalcNation's HTML Formatter runs 100% in your browser — no upload, no server, no login.

All Features

Format — Beautify with 2/4 spaces or tab indent. Minify — Compress HTML, remove whitespace. Validate — W3C-style syntax checking with line numbers. Live Preview — Sandboxed iframe rendering. HTML → JSX — class→className, style objects. HTML → React — Full React component with TypeScript. HTML → Vue — Vue SFC with script setup. HTML → Markdown — Convert headings, links, lists. Accessibility Audit — WCAG 2.1 checks. SEO Checker — Title, meta, H1, OG tags. Security Scanner — XSS risks, inline handlers. Performance Score — Defer, lazy load, inline JS. AI Explain — Plain English description. AI Auto-Fix — Claude fixes all issues automatically. AI Generate — Describe HTML, get code. CSS/JS Extractor — Pull out styles and scripts. Snippet Export — HTML, JS string, TS const. Structure Map — Visual tag hierarchy. Duplicate ID Detector — Flag same IDs. Template Variable Scanner — Find { {vars}}.

Frequently Asked Questions

What is an HTML Formatter?

An HTML Formatter beautifies raw or minified HTML code by adding proper indentation, line breaks and spacing, making it easy to read and edit. It also validates syntax and checks for accessibility and SEO issues.

Is this HTML Formatter free?

Yes, 100% free. All processing happens in your browser — no upload, no login, no server.

What is HTML to JSX conversion?

JSX is the HTML-like syntax used in React components. Converting HTML to JSX changes class to className, for to htmlFor, and adds self-closing tags for void elements like <br/> and <img/>.

What does the Accessibility Audit check?

It checks for missing alt attributes on images, missing aria-label on buttons, improper heading order, missing lang attribute, and other WCAG 2.1 issues.