⚙️ XML Formatter & Validator

How to Use the XML Formatter & Validator

Using our free XML Formatter is straightforward. Simply paste your raw, poorly formatted, or minified XML into the Input XML panel on the left, then click the Format & Validate button to instantly receive a properly indented, human-readable version in the Formatted Output panel.

Step-by-Step Guide

1. Paste your XML — Copy any XML string and paste it into the left editor panel.
2. Click "Format & Validate" — The tool will simultaneously format the XML with proper indentation and validate its structure.
3. Review the result — If your XML is valid, you'll see the formatted output on the right and a ✓ Valid XML badge. If there are errors, they'll be listed clearly below the toolbar.
4. Copy the output — Use the ⎘ Copy button in the output panel header to copy the formatted XML to your clipboard.
5. Use "Load Sample" — If you want to try the tool without your own data, click 📄 Load Sample to insert a working XML example.

What is XML Validation?

XML (eXtensible Markup Language) validation ensures a document conforms to specific structural rules. There are two levels of XML correctness:

1. Well-Formed XML

A well-formed XML document follows the basic syntactic rules of the XML specification:

• Single root element — The entire document must be wrapped in one root element (e.g., <root>...</root>).
• Properly closed tags — Every opening tag must have a matching closing tag. <item>value</item> is correct; <item>value is not.
• Case sensitivity — XML tag names are case-sensitive. <Title> and <title> are treated as different elements.
• Proper nesting — Tags must not overlap. <a><b></a></b> is invalid. Correct: <a><b></b></a>.
• Quoted attributes — Attribute values must always be in quotes: <book id="1"> not <book id=1>.
• Special characters escaped — Characters like <, >, &, ", ' in text content must be escaped as <, >, &, ", '.

Code Snippets

Parse and Validate XML in JavaScript (Browser)

// Using the native DOMParser API — no libraries needed
function validateXml(xmlString) {
  const parser = new DOMParser();
  const doc = parser.parseFromString(xmlString, 'application/xml');
  const parserError = doc.querySelector('parsererror');
  if (parserError) {
    return { valid: false, error: parserError.textContent };
  }
  return { valid: true, error: null };
}

Format XML with Proper Indentation in Node.js

function formatXml(xml) {
  let formatted = '';
  let indent = 0;
  const tab = '  ';
  xml.replace(/>\s*</g, '><')
     .split(/(<[^>]+>)/)
     .filter(Boolean)
     .forEach(node => {
       if (node.match(/^<\//)) {
         indent--;
         formatted += tab.repeat(Math.max(indent, 0)) + node + '\n';
       } else if (node.match(/^<[^?!].*[^/]>$/)) {
         formatted += tab.repeat(indent) + node + '\n';
         indent++;
       } else {
         formatted += tab.repeat(indent) + node.trim() + '\n';
       }
     });
  return formatted;
}

Deep Dive: XML Schemas vs. Well-Formedness

When validating XML, developers often confuse well-formedness with schema validation. Well-formedness simply means that the XML parser can read the document hierarchy without crashing. Schema validation, on the other hand, checks whether the elements, structures, and data types conform to a strict template defined by a Document Type Definition (DTD) or an XML Schema Definition (XSD).

For example, a schema might enforce that an <age> element must contain only positive integers, or that a <product> element must contain exactly one <price> element. While our browser-based tool validates well-formedness, complex enterprise systems usually perform both checks to guarantee data integrity across legacy integrations.