XML Formatter & Validator

XML Formatter and Validator

XML is easy for systems to read but difficult to review when it arrives as one long line. This formatter checks whether a document is well formed, then beautifies it with consistent indentation or minifies it by removing unnecessary whitespace between tags. Processing happens in your browser.

Well-formed XML

A well-formed document has one root element, correctly nested tags, quoted attributes, and matching opening and closing tags. Empty elements use />. The formatter preserves comments and processing instructions while changing layout.

<catalog>
  <item id="1">Example</item>
</catalog>

Well-formedness is different from schema validation. An XSD, DTD, or application validator is still required to check required fields, allowed values, and business rules.

Beautify and minify modes

Mode	Best for	What changes
Beautify	Reviews, debugging, version control	Adds line breaks and selectable indentation
Minify	Network transfer, caches, compact storage	Removes inter-tag whitespace and condenses whitespace

Beautify mode supports two spaces, four spaces, and tabs. Minify mode keeps the XML structure and removes presentation whitespace; review the result before using it where text-node whitespace is significant.

Common XML errors

Error	Example	Fix
Mismatched tags	<item></catalog>	Close elements in reverse nesting order
Unclosed element	<catalog><item>	Add closing tags or use a self-closing element
Unquoted attribute	<item id=1 />	Use <item id="1" />
Multiple roots	<a /><b />	Wrap content in one root element
Unescaped text	<name>A & B</name>	Encode ampersands as &amp;

Comments and declarations

Comments, XML declarations, CDATA sections, and processing instructions are part of XML syntax and should not be removed casually. A declaration commonly appears at the start:

<?xml version="1.0" encoding="UTF-8"?>
<message><!-- kept for reviewers --><![CDATA[raw <text>]]></message>

Formatting improves readability but does not sanitize XML. Treat untrusted XML as data and use a parser with external entity processing disabled on the server.

Code examples

JavaScript

const parser = new DOMParser();
const document = parser.parseFromString(xmlText, "application/xml");
const error = document.querySelector("parsererror");

if (error) {
  console.error("Invalid XML");
}

Python

import xml.etree.ElementTree as ET

root = ET.fromstring(xml_text)
ET.indent(root, space="  ")
formatted = ET.tostring(root, encoding="unicode")

Command line

xmllint --format input.xml > formatted.xml
xmllint --noblanks input.xml > minified.xml

XML formatter compared with related tools

Tool	Primary purpose	Schema-aware
XML formatter	Readable or compact layout	No
XML validator	Syntax and well-formedness errors	Usually no
XSD validator	Contract and data-type validation	Yes
JSON formatter	JSON layout and syntax checks	No

Use this formatter for quick browser-based cleanup. Use a project validator or CI check for production documents, namespaces, schemas, and security-sensitive parsing.

Common uses

• Reviewing API payloads and configuration files
• Comparing XML files in pull requests
• Preparing SOAP or RSS documents for debugging
• Reducing payload size before transfer
• Teaching XML nesting and syntax

Formatting does not change the intended data model, but whitespace can be meaningful in mixed-content XML. Test documents containing human-readable text, xml:space="preserve", or CDATA in the target application.