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HTML Formatter

HTML (HyperText Markup Language) is the standard markup language for web pages. This tool formats HTML with proper indentation, minifies it for production, extracts metadata (title, description, Open Graph tags), and validates common issues like missing alt attributes or deprecated tags.

Specifications

Common Use Cases

  • Format minified HTML from view-source or API responses
  • Optimize HTML size before deployment
  • Audit page metadata for SEO (title, description, OG tags)
  • Debug HTML structure and nesting issues
  • Validate accessibility basics (alt attributes)
  • Prepare HTML snippets for documentation

Features

  • Pretty-print HTML with consistent indentation
  • Minify HTML for production (remove whitespace, comments)
  • Extract page metadata (title, description, charset)
  • Parse Open Graph tags for social media previews
  • Count scripts and stylesheets
  • Validate common HTML issues (missing alt, deprecated tags)
  • Show size comparison between original and minified

Examples

Web Page with Metadata

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A complete HTML document with head metadata and body content.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="description" content="A sample web page for testing">
  <meta property="og:title" content="Sample Page">
  <meta property="og:description" content="This is a sample page">
  <title>Sample Page</title>
  <link rel="stylesheet" href="styles.css">
</head>
<body>
  <header>
    <h1>Welcome</h1>
    <nav>
      <a href="/">Home</a>
      <a href="/about">About</a>
    </nav>
  </header>
  <main>
    <p>Hello, world!</p>
  </main>
  <script src="app.js"></script>
</body>
</html>

HTML Snippet

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A component or partial HTML fragment.

<div class="card">
  <img src="image.jpg" alt="Card image">
  <div class="card-body">
    <h2 class="card-title">Card Title</h2>
    <p class="card-text">Some description text here.</p>
    <button class="btn btn-primary">Learn More</button>
  </div>
</div>

Tips

  • Use the minified version for production to reduce page load time.
  • Open Graph tags control how your page appears when shared on social media.
  • The description meta tag is important for SEO and search result snippets.
  • Always include alt attributes on images for accessibility.
  • Use semantic HTML elements (header, main, nav, article) for better structure.

Understanding HTML

HTML (HyperText Markup Language) is the foundational language of the web. Every web page is an HTML document -- a tree of elements that browsers parse and render into the visual interfaces billions of people interact with daily. The current version, maintained by WHATWG as a Living Standard, evolves continuously rather than through numbered releases.

HTML provides the semantic structure of a page. Elements like <header>, <nav>, <main>, <article>, and <footer> convey meaning to browsers, screen readers, and search engines. The <head> section contains metadata: the document title, character encoding, viewport settings, stylesheets, scripts, Open Graph tags for social sharing, and structured data for SEO. The <body> contains the visible content.

Modern HTML extends far beyond simple markup. The <canvas> element enables 2D and 3D graphics. The <video> and <audio> elements provide native media playback. Web Components (<template>, <slot>, custom elements) allow reusable encapsulated widgets. Form elements support client-side validation with attributes like required, pattern, min, and max. Semantic elements improve accessibility by giving assistive technologies a clear document outline.

For developers, HTML is rarely written by hand at scale. Frameworks like React, Vue, Svelte, and Astro generate HTML from component templates. Server-side rendering produces HTML on the server for faster initial page loads. Static site generators pre-build HTML at deploy time. Despite this abstraction, understanding the output HTML is essential for debugging layout issues, optimizing performance, ensuring accessibility compliance, and diagnosing SEO problems.

HTML is forgiving of syntax errors — browsers will render unclosed tags and missing quotes as best they can. XHTML, by contrast, applies strict XML rules: all tags must be closed, attribute values must be quoted, and elements must be properly nested. XHTML was popular in the early 2000s, but the WHATWG HTML Living Standard returned to the more lenient HTML parsing model. Today, writing well-formed HTML that would also be valid XHTML is considered best practice, even though browsers do not require it.

Open Graph (og:) meta tags control how a page appears when shared on social media platforms like Facebook, LinkedIn, and Twitter. Key tags include og:title, og:description, og:image, and og:url. Twitter has its own twitter:card tags that override Open Graph when present. Without these tags, platforms will attempt to guess the title and image, often with poor results. Semantic HTML elements like <nav>, <main>, <article>, and <aside> serve a related purpose — they communicate the structure and meaning of content to browsers, screen readers, and search engines. Using semantic elements improves accessibility for users with disabilities, helps search engines understand page hierarchy, and makes the codebase more maintainable.

HTML minification removes unnecessary characters without changing functionality: whitespace between tags, HTML comments, optional closing tags, redundant attributes, and unnecessary quotes around attribute values. This reduces file size and improves page load time, with typical savings of 10-30% before gzip compression. Tools like html-minifier-terser handle this automatically in build pipelines, making it a straightforward optimization for production deployments.

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