HTML Formatter Online

A lightweight HTML formatter that produces clean, properly indented markup for developers, editors, and QA professionals.

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1,748+

Total Calculations Run

< 15ms

Browser Execution Speed

100%

Client-Side Privacy

4.9 / 5.0

User Satisfaction

Worked Example & Common Values

Below is a sample worked calculation demonstrating how HTML Formatter Online processes input data instantly inside your browser.

Sample Input Minified string: {"id":1,"status":"active","roles":["admin"]}

Computed Result

{
  "id": 1,
  "status": "active",
  "roles": [
    "admin"
  ]
}

Execution Mode Client-Side In-Browser JS

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About This Tool

The tool formats an HTML string into a consistent, readable markup. It parses the input into a tolerant DOM-like structure, preserves element semantics and script/style boundaries, and then re-emits the code with a defined style. It supports common HTML5 concepts, including void elements and proper nesting, and can preserve or omit comments based on options. The default result emphasizes readability across editors and review workflows, reducing diffs caused by incidental whitespace.
Conceptually, formatting involves three steps: parse, normalize, and emit. The parser accepts imperfect markup and normalizes it without altering functionality. Normalization applies indentation (default 2 spaces), optional attribute wrapping, and uniform line endings. The emitter outputs stable, deterministic markup where attributes and elements follow a predictable order, while scripts and style blocks remain untouched to avoid breaking behavior. Optional validation hints surface if the input has structural issues.
Who benefits include front-end developers, content producers, and QA engineers who exchange HTML fragments. Unique value lies in deterministic output independent of editor and easy integration into pipelines. Core features include adjustable indentation, attribute wrapping, line-ending control, and support for HTML5. Use cases include preparing HTML for code reviews, generating clean diffs, and cleaning legacy markup before migration to modern templates.

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How to Use

Provide inputs: paste HTML into the html_input field.
Choose options: set indent size, wrap attributes, and line endings.
Run formatting: click the format button to produce formatted output.
Review outputs: inspect the formatted_html output and any warnings.
Copy/download: copy to clipboard or save as a file.

Frequently Asked Questions

Find Quick Answers

What input formats are supported?

The tool accepts raw HTML strings and handles typical HTML5 markup, including nested elements and void elements. It does not fetch remote resources or execute embedded scripts; cross-file dependencies are not resolved.

Does it preserve comments and DOCTYPE?

Comments can be preserved or stripped based on options. DOCTYPE handling preserves the intent of the document header when present, but the formatter primarily reworks whitespace and indentation without altering document type declarations.

Can I customize indentation and line endings?

Yes. You can set indent_size (e.g., 2 or 4 spaces) and choose line ending style (LF or CRLF). These settings influence how the output is emitted without changing semantics.

Is the output validated?

The tool performs structural formatting validation to ensure well-formed markup. It does not execute scripts or CSS, and it does not guarantee external resource validity; it focuses on syntactic correctness and readability.

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