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HTML Formatter Online — Free HTML Beautifier & Minifier

HTML Formatter

Format, minify, and validate HTML with attribute sorting and template support.

Free online HTML formatter, beautifier, minifier, and validator powered by js-beautify. Format unorganized, minified, or CMS-generated HTML with customizable 2-space, 4-space, or tab indentation, automatic attribute wrapping, and alphabetical attribute sorting for clean Git diffs. Includes real-time HTML5 syntax validation (detecting unclosed tags, duplicate IDs, missing alt attributes), seamless HTML-to-JSX conversion for React components, embedded CSS/JavaScript code formatting, and robust template syntax preservation for Handlebars, EJS, and Jinja. Runs 100% client-side in your browser with zero data transmission, guaranteeing complete privacy for sensitive markup.

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Tags: html, format, beautify, minify, validate, prettify, jsx, beautifier, minifier, template, handlebars, ejs

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HTML Formatter is also known as: HTML Beautifier Online, HTML Minifier Online, HTML Validator Online, HTML to JSX Converter, Online HTML Prettifier, HTML Code Formatter, HTML Indenter Online, HTML Cleanup Tool, HTML Attribute Sorter, HTML Syntax Formatter.

How to HTML Formatter Online

  1. Paste your raw, minified, or malformed HTML into the input editor, or click Upload to select an .html or .htm file from your local disk.

  2. Select your desired indentation format (2 spaces, 4 spaces, or hard tabs) and configure attribute wrapping rules to match your codebase style guides.

  3. Optionally toggle "Sort Attributes" to alphabetically order tag attributes for cleaner, deterministic version control diffs.

  4. Click "Format" or press ⌘↵ (Ctrl+Enter) to instantly beautify markup with automated tag alignment, structural indentation, and syntax highlighting.

  5. Switch actions on demand: execute "Minify" to collapse markup for production delivery, run "Validate" to diagnose unclosed tags and duplicate IDs, or convert markup to React components with "→ JSX".

  6. Copy the cleaned output with ⌘⇧C, download as a standalone .html file, or generate a gzip-compressed shareable link for peer review.

HTML Formatter Features

  • Configurable Indentation Engine: Switch seamlessly between 2-space, 4-space, or native tab indentation conforming to Prettier and team style specifications.

  • 5 Attribute Wrapping Strategies: Control attribute density with Auto (wrap on column limit), Force (one attribute per line), Force-Expand (multiline expansion on all elements), Force-Aligned (vertical alignment under initial attribute), or Preserve original layout.

  • Alphabetical Attribute Sorting: Normalizes attribute ordering across elements (e.g. class, id, src, type) to minimize merge conflicts and improve code review readability.

  • Production HTML Minification: Strips superfluous whitespace, line breaks, HTML comments, and redundant tokens to minimize over-the-wire payload size and optimize Core Web Vitals.

  • Real-Time Structural HTML5 Validator: Audits tag hierarchies to catch unclosed elements, mismatched nesting pairs, duplicate id attributes, void tag errors, and missing image alt attributes.

  • Automated HTML to JSX/TSX Conversion: Transpiles HTML tags to React JSX by mapping class to className, for to htmlFor, inline style strings to camelCase JavaScript objects, and void tags to self-closing syntax.

  • CMS & Email Cleanup Utility: Strips legacy presentational elements (<font>, <center>, <marquee>), empty tags, and inline style cruft exported from WYSIWYG rich text editors.

  • Embedded CSS & JavaScript Beautification: Automatically detects and independently formats code inside <style> and <script> blocks according to language-specific formatting rules.

  • Template Syntax Preservation: Protects Handlebars ({{ }}), EJS (<% %>), and Jinja/Twig/Django ({% %}) template directives as atomic tokens without interrupting HTML hierarchy.

  • Visual Syntax Highlighting: Color-coded token rendering for DOCTYPE declarations, HTML tags, attribute names, string values, HTML entities, and template expressions.

  • Document Type Auto-Detection: Automatically distinguishes between complete HTML documents (with <!DOCTYPE> and <html>), partial component fragments, and template files.

  • Real-Time Document Statistics: Computes total element counts, maximum DOM nesting depth, and UTF-8 output byte weights with real-time badge updates.

  • Gzip-Compressed Shareable URLs: Serializes document state into URL fragments using lightweight compression for instant bug reporting and team collaboration.

  • Large-Input Performance Guard: Provides real-time byte count metrics and non-blocking background processing for multi-megabyte HTML files.

  • Power User Keyboard Navigation: Accelerate workflows with ⌘↵ (Format), ⌘⇧F (Force Format), ⌘⇧M (Minify), ⌘⇧V (Validate), ⌘⇧K (Clear), and ⌘⇧C (Copy).

  • 100% Client-Side Privacy: Complete parsing, tokenization, and minification execute entirely inside browser memory with zero server API calls.

Supported Formats & Dialects

The HTML Formatter supports 6 syntax formats and dialects for accurate parsing and processing.

Standard HTML5 Markup (WHATWG Living Standard)
The modern web standard featuring semantic elements (<article>, <section>, <nav>, <main>), custom elements, void tags, and standard <!DOCTYPE html> document root declarations.
XHTML & Strict XML Compliance
Strict XML-based HTML dialect requiring lowercase element names, quoted attribute values, well-formed hierarchy nesting, and explicit self-closing tags (<img />, <br />).
React JSX & TSX Component Templates
Component markup dialect using className, htmlFor, camelCase event handlers (onClick, onChange), inline style objects (style={{ color: "red" }}), and self-closing void elements.
Handlebars & Mustache Logic-Less Templates
Templating dialect utilizing double and triple curly brace delimiters ({{#if user}}, {{name}}, {{/if}}, {{> partial}}) that require atomic preservation during tag indentation.
Embedded JavaScript (EJS) & ERB Templates
Server-side rendering templates utilizing scriptlet tags (<% if (auth) { %>, <%= title %>, <%- rawMarkup %>) parsed without corrupting enclosing HTML tree hierarchy.
Jinja, Twig & Django Template Syntax
Python and PHP templating standard featuring block statements ({% for item in list %}, {% block content %}, {{ item.id }}) formatted seamlessly alongside HTML structural nodes.

In-Depth Technical Guides

All Guides
text data

Clean HTML to Markdown for LLM & RAG Pipelines: Token Minimization & Semantic Table Extraction

Strip DOM boilerplate, convert complex HTML tables and semantic trees into clean Markdown, slash RAG embedding token costs by 60–80%, and preserve critical context for LLMs.

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HTML Entity Encoding & Escaping: XSS Prevention, Unicode & Parser Nuances

Master HTML entity encoding, numeric character references, context-aware XSS escaping in body vs attributes vs JS, and HTML5 named entity parser rules.

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Mastering CSS Selectors: Specificity Math, Relational :has(), and Modern Pseudo-Classes

A comprehensive developer guide to CSS selectors, specificity calculation mechanics, the :has() relational selector, forgiving selector lists, and high-performance DOM querying.

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SVG Optimization & Sanitization: Production SVGO Configs, viewBox & XSS Hardening

Strip metadata bloat and invisible paths using SVGO, sanitize malicious script tags and inline event handlers to prevent SVG-based XSS, and configure responsive viewBox scaling.

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WCAG 2.2 Accessibility Audit Checklist: Automated & Manual Testing Guide

A comprehensive developer guide to WCAG 2.2 accessibility compliance: new success criteria, color contrast ratios, keyboard navigation, ARIA patterns, and CI/CD audit workflows.

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XML Formatting, Validation & XXE Prevention: The Production Engineering Guide

Master XML formatting standards, well-formedness rules vs XSD validation, namespace resolution, CDATA handling, and server-side XXE attack prevention.

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Related Standards & RFC Specifications

All Standards
HTML (HyperText Markup Language)Web Standards

HTML is the standard markup language for creating web pages and web applications, structuring content through semantic elements and the DOM.

HTML Entities & Character EncodingWeb Development

HTML entities are coded character strings starting with an ampersand and ending with a semicolon used to render reserved and special characters in HTML.

XML (Extensible Markup Language)Data Formats

XML is a flexible, tag-based markup language standardized by the W3C for storing and transporting structured, machine-parseable hierarchical data.

Frequently Asked Questions

How does client-side HTML AST tokenization and formatting work in DevFlow?
DevFlow utilizes an in-browser tokenizer and abstract syntax tree (AST) parser powered by js-beautify. The engine tokenizes raw HTML markup into opening tags, closing tags, attribute value pairs, text nodes, and template delimiters. It tracks nesting depth using an internal tag stack, calculates appropriate indentation based on user-selected tab or space counts, normalizes newlines, and serializes the tree back into clean, uniformly formatted HTML without sending any data over the network.
What are the differences between the 5 attribute wrapping modes (Auto, Force, Force-Expand, Force-Aligned, Preserve)?
The 5 attribute wrapping modes provide granular control over markup formatting: 1) Auto wraps attributes onto subsequent lines only when the line length exceeds the configured wrap threshold; 2) Force places each attribute on its own dedicated newline whenever an element has multiple attributes; 3) Force-Expand places every attribute on a new line regardless of element size or count; 4) Force-Aligned breaks attributes onto new lines and indents them so they align vertically with the first attribute column; and 5) Preserve maintains the original line breaks from your input text.
How does alphabetical attribute sorting improve Git pull request diffs and CI/CD code reviews?
When multiple developers work on shared HTML templates or component markup, attributes are frequently added in arbitrary orders (e.g. <div class="a" id="b" data-role="c"> vs <div id="b" data-role="c" class="a">). Alphabetical attribute sorting normalizes all element attributes deterministically (<div class="a" data-role="c" id="b">). This prevents spurious line modifications in Git commits, minimizes merge conflicts, and simplifies automated code reviews across team codebases.
How does the HTML to JSX converter transform standard HTML markup into React components?
The HTML-to-JSX transpilation engine applies automated transformations required by React and JSX specifications: it converts standard HTML class attributes to className, for attributes on <label> elements to htmlFor, transforms inline CSS style strings into camelCase JavaScript key-value objects (e.g. style="margin-top: 10px; font-size: 14px" becomes style={{ marginTop: "10px", fontSize: "14px" }}), converts HTML comment blocks (<!-- ... -->) into JSX comments ({/* ... */}), and ensures all HTML5 void elements (<img />, <input />, <br />) are explicitly self-closing.
How does the formatter preserve template expressions like Handlebars, EJS, and Jinja without syntax errors?
Standard HTML formatters often corrupt template expressions by treating delimiters like {{, <%, or {% as regular text nodes or invalid tag brackets. DevFlow employs specialized lexer rules that recognize Handlebars/Mustache expressions ({{#if}}, {{/if}}), EJS scriptlets (<% ... %>), and Jinja/Django tags ({% for ... %}) as opaque tokens. The engine maintains proper structural indentation around these blocks while leaving the inner template syntax and variables untouched.
What syntax errors, accessibility issues, and deprecations does the HTML validator detect?
The validator parses the document to detect: 1) Structural Errors: unclosed tags, mismatched closing tags, void tags with illegal closing tags, and invalid nesting; 2) Duplicate IDs: duplicate id="..." attribute values that violate DOM uniqueness and break accessibility landmarks; 3) Accessibility Warnings: <img> tags missing required alt attributes for screen readers and <a> tags without href targets; and 4) Deprecated Tags: obsolete presentational elements such as <font>, <center>, <marquee>, <strike>, and <blink>.
How does the formatter beautify embedded CSS (<style>) and JavaScript (<script>) blocks?
When encountering <style> or <script> containers, the formatter temporarily switches parsing context. It routes CSS rules through an embedded CSS formatter that indents selectors, properties, and media queries, while JavaScript code is processed through a JS beautifier that normalizes variable declarations, function scopes, and control flow blocks. The embedded code blocks are indented relative to their parent HTML container before being reassembled into the document.
What is the difference between aggressive HTML minification and conservative whitespace collapsing?
Aggressive HTML minification strips all non-essential whitespace between elements (> < becomes ><), removes HTML comments, and collapses multi-space runs within text nodes to produce the smallest possible payload for production distribution. Conservative whitespace collapsing protects delicate inline phrasing elements (such as <span>, <a>, and <strong>) by preserving a single space delimiter between adjacent inline tags, preventing accidental concatenation of adjoining words during browser text layout.
How does the HTML cleanup engine sanitize markup generated by CMS editors and email builders?
CMS rich text editors (such as WordPress, TinyMCE, or CKEditor) and email builders often generate noisy, deprecated markup. The cleanup engine performs multi-pass sanitization: it converts legacy tags (<font>, <center>, <strike>) to semantic HTML5 alternatives (<span>, <div>, <s>), removes redundant empty containers (<div></div>, <span></span>), and strips unwanted inline style declarations or data-* attributes, returning clean, maintainable markup.
Why do HTML5 void elements differ from XHTML/XML self-closing tags, and how are they handled?
Under the WHATWG HTML5 specification, void elements (such as <br>, <hr>, <img>, <input>, <link>, and <meta>) can never contain child nodes and do not require a closing slash. In contrast, XHTML and JSX require all elements to be explicitly closed with a self-closing trailing slash (<br />, <img />). DevFlow respects HTML5 conventions in standard formatting mode while automatically adding self-closing syntax when converting markup to JSX or formatting for strict XML pipelines.

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