XML Formatter

Introduction

The XML Formatter tool (XML Beautifier) converts messy, single-line, or compressed XML strings into a readable format with clear hierarchical indentation. Built on PHP's built-in DOMDocument component, it first automatically validates XML syntax, then expands elements in a tree structure using standard 4-space indentation to clearly display tag nesting relationships.

Formatted XML shows clear hierarchical indentation for each tag, making parent-child relationships immediately visible. The tool automatically removes the XML declaration header (<?xml ... ?>), keeping only the root element and its content for cleaner output. It also validates XML syntax to help developers discover unclosed tags, malformed attributes, and other issues during formatting.

Technical Principles

XML (Extensible Markup Language) is a W3C-standardized markup language widely used for data exchange and document storage. Its core structures include: Elements, Attributes, Text Content, Comments, and Processing Instructions.

The XML formatting process involves: Lexical Analysis - splitting the XML string into tokens (tags, attributes, text) → DOM Parsing - building a Document Object Model (DOM Tree) → Re-serialization with formatOutput enabled for beautified output. The DOM parser uses the libxml2 library, which automatically detects syntax issues such as unclosed tags, unquoted attribute values, and incorrect encoding declarations, returning precise error information. After formatting, the tool uses a regular expression to remove the XML declaration header, producing clean output starting from the root element.

Use Cases

• View and debug XML response data from SOAP web services and REST APIs
• Edit XML configuration files in Java projects: pom.xml, web.xml, struts.xml, mybatis-config.xml
• Process standard XML formats like SVG graphics, RSS feeds, and sitemap.xml
• Troubleshoot XML parsing errors by locating unclosed tags or attribute issues
• Format XML data examples in API documentation during frontend-backend integration
• Handle AndroidManifest.xml and layout XML files in Android development

Frequently Asked Questions

Q: What if XML formatting shows "StartTag: invalid element name" errors?

A: This means the input XML has malformed element names. Common causes include disallowed special characters in tag names, tag names starting with digits, or mismatched angle brackets. Check the XML content for non-compliant tag names.

Q: What's the difference between XML and HTML?

A: XML is data-oriented with customizable tags and strict syntax (all tags must close, attribute values must be quoted, case-sensitive). HTML is presentation-oriented with predefined tags and looser syntax (allows unclosed tags, unquoted attribute values, etc.).

Q: Why is the XML declaration header (<?xml version="1.0"?>) removed from the output?

A: The tool removes the declaration header by default for cleaner output. If you need to keep the declaration, simply include it in the input — the tool will still parse and format the content correctly.

Typical Usage

Input (compressed XML):

<bookstore><book category="programming"><title lang="en">PHP: From Beginner to Master</title><author>John Smith</author><price currency="USD">39.99</price></book><book category="database"><title lang="en">MySQL in Action</title><author>Jane Doe</author><price currency="USD">29.99</price></book></bookstore>

Output (formatted XML):

<bookstore>
    <book category="programming">
        <title lang="en">PHP: From Beginner to Master</title>
        <author>John Smith</author>
        <price currency="USD">39.99</price>
    </book>
    <book category="database">
        <title lang="en">MySQL in Action</title>
        <author>Jane Doe</author>
        <price currency="USD">29.99</price>
    </book>
</bookstore>

Related Tools

XML Formatter works alongside HTML Formatter as both belong to markup language beautification tools used together in web development. JSON Formatter handles JSON data format, commonly used alongside XML for data exchange scenarios. SQL Formatter belongs to the same code beautification tool family and is essential for database query development. Additionally, JS Formatter and CSS Formatter are part of the code beautification tool stack that frontend developers can use together.