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HTML Formatter & Viewer

Format or minify HTML with adjustable indentation, preview the rendered page, and flag unclosed tags, duplicate IDs and missing alt text.

HTML Formatter & Viewer

Indent:
View:
880 bytes / 34 lines / 29 tags
Formatted output1,484 bytes / 68 lines / Depth: 7
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>
      Sample Page
    </title>
  </head>
  <body>
    <header class="header" style="background-color:#333;color:#fff;padding:20px">
      <h1 id="main-title">
        Welcome to HTML Formatter
      </h1>
      <nav>
        <ul>
          <li>
            <a href="#home">
              Home
            </a>
          </li>
          <li>
            <a href="#about">
              About
            </a>
          </li>
          <li>
            <a href="#contact">
              Contact
            </a>
          </li>
        </ul>
      </nav>
    </header>
    <div>
      <section id="content">
        <article>
          <h2>
            About This Tool
          </h2>
          <p>
            This tool formats, beautifies, and validates HTML code with live preview.
          </p>
          <img src="https://example.com/hero.png" alt="Product screenshot">
          <ul>
            <li>
              Format and beautify HTML
            </li>
            <li>
              Minify for production
            </li>
            <li>
              Live preview
            </li>
            <li>
              Validation warnings
            </li>
          </ul>
        </article>
      </section>
    </div>
    <footer>
      <p>
        &copy; 2026 HTML Formatter
      </p>
    </footer>
  </body>
</html>

No validation issues

Minified HTML
847 bytes (4% smaller)
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Sample Page</title></head><body><header class="header" style="background-color:#333;color:#fff;padding:20px"><h1 id="main-title">Welcome to HTML Formatter</h1><nav><ul><li><a href="#home">Home</a></li><li><a href="#about">About</a></li><li><a href="#contact">Contact</a></li></ul></nav></header><div><section id="content"><article><h2>About This Tool</h2><p>This tool formats, beautifies, and validates HTML code with live preview.</p><img src="https://example.com/hero.png" alt="Product screenshot"><ul><li>Format and beautify HTML</li><li>Minify for production</li><li>Live preview</li><li>Validation warnings</li></ul></article></section></div><footer><p>&copy; 2026 HTML Formatter</p></footer></body></html>

Statistics

29
HTML tags
7
Max depth
0.9KB
File size
34
Lines

Updated . Provided as is. Check the output before you rely on it in production.

How to use HTML Formatter & Viewer

  1. 1

    Paste your HTML

    Paste minified or unformatted HTML. Fragments and complete documents both work.

  2. 2

    View formatted output

    Formatted HTML appears in the right panel with consistent indentation and line breaks. Switch views to see the live preview or minified output.

  3. 3

    Check validation issues

    The Validation Issues panel lists problems such as unclosed tags and invalid nesting.

  4. 4

    Copy or download

    Copy the formatted HTML or download it as an .html file.

Questions and answers

What is HTML Formatter & Viewer?
An HTML formatter re-indents markup so its nesting is readable, and a minifier strips that whitespace back out. This tool does both with adjustable indentation and attribute wrapping, renders a live preview, and flags unclosed or mismatched tags, duplicate IDs, images without alt text and deprecated tags.
Does HTML Formatter & Viewer store or send my data?
No. Processing happens directly in your browser. Your HTML never leaves your device.
Does it validate HTML for errors?
Yes. It checks for common problems such as unclosed tags and improper nesting and lists them in the Validation Issues panel.

Use it as an API

HTML Formatter & Viewer is also callable as a free HTTP JSON API at https://aidevhub.io/api/html-formatter/ — GET with query parameters or POST with a JSON body, no authentication, CORS enabled, fair use (abusive traffic is throttled at the edge; there is no per-request quota header). Responses return { ok, tool, result, meta }. 

curl -s -X POST https://aidevhub.io/api/html-formatter/ \
  -H "Content-Type: application/json" \
  -d '{"html":"<div><p>Hello</p><span>world</span></div>","mode":"format"}'

Machine-readable contract: /api/tool/html-formatter.json All API endpoints: /agents/ LLM site index: /llms.txt

For AI agents: how to call this tool

Machine-readable contract, endpoints and examples. Humans can ignore this section.

Best Path For Builders

Dedicated API endpoint

Deterministic outputs, machine-safe contracts, and production-ready examples.

Dedicated API

https://aidevhub.io/api/html-formatter/

OpenAPI: https://aidevhub.io/api/openapi.yaml

GET /api/html-formatter/ GET html-formatter
POST /api/html-formatter/ POST html-formatter