XML Formatter

What formatting preserves

• XML declaration (<?xml version="1.0" encoding="UTF-8"?>) kept verbatim.
• DOCTYPE declarations and internal subsets preserved.
• Processing instructions (<?xml-stylesheet ?>) kept on their own line.
• Comments on their own line or inline depending on context.
• CDATA sections preserved exactly including whitespace inside.
• Attribute values re-quoted using double quotes if they contain no double quotes, single quotes otherwise.
• Entity references like &, <, > left as-is unless you enable full entity expansion.

Indentation examples

Input (minified):

<books><book id="1"><title>1984</title><author>George Orwell</author></book></books>

Formatted (2 spaces):

<books>
  <book id="1">
    <title>1984</title>
    <author>George Orwell</author>
  </book>
</books>

Common errors the tool catches

Well-formed vs valid

• Well-formed XML follows the syntactic rules: balanced tags, valid characters, proper nesting. The formatter checks this.
• Valid XML additionally conforms to a schema (DTD or XSD). For that, use the XSD validator.

An XML document can be well-formed without being valid, but not the other way around.

Practical notes

• XML attribute order is meaningful to some systems (not many modern ones), the formatter preserves input order.
• Self-closing vs explicit empty tags: <foo/> and <foo></foo> are equivalent in XML; the formatter uses self-closing for empty elements unless you opt out.
• Namespace prefixes are preserved exactly.