Free Online XML Validator

What is an XML Validator?

An XML validator is a tool that checks XML (Extensible Markup Language) documents for well-formedness and validity according to XML syntax rules and optionally against a schema or DTD (Document Type Definition). It ensures that XML documents are correctly structured and can be reliably processed by XML parsers and applications.

How XML Validation Works

XML validation involves checking documents at two distinct levels:

1. Well-formedness validation ensures the document follows basic XML syntax rules
2. Schema validation (optional) checks the document against a defined structure
3. Parsing the XML document to create a Document Object Model (DOM)
4. Checking element nesting, attribute formatting, and entity references
5. Validating against namespaces and other XML specifications when applicable

By validating XML, developers can catch errors early in development, ensure interoperability between systems, and maintain data integrity throughout processing pipelines.

Key Features of Our XML Validator

• Comprehensive well-formedness checking
• Detailed error reporting with line and column numbers
• Highlighting of problematic code sections
• Support for XML namespaces
• Client-side processing (your data never leaves your browser)
• Large XML document support
• Immediate feedback on XML syntax issues

Common Use Cases

• Debugging XML configurations before deployment
• Verifying SOAP API requests and responses
• Checking XML data before importing into systems
• Validating XML outputs from data exports
• Testing XML documents during development
• Ensuring compliance with XML standards
• Troubleshooting XML parsing errors

Common XML Validation Errors

Being aware of common XML errors can help you fix validation issues quickly:

• Unclosed Tags: Elements must have matching opening and closing tags
• Improper Nesting: Elements must be properly nested (no overlapping tags)
• Missing Root Element: XML documents must have exactly one root element
• Unquoted Attributes: Attribute values must be enclosed in quotes
• Invalid Characters: Some characters (like < and &) must be escaped in content
• Undefined Namespaces: Namespace prefixes must be declared before use
• Incorrect Encoding: XML declaration must match the actual document encoding

<?xml version="1.0" encoding="UTF-8"?>
<library>
  <book id="b1">
    <title>The Great Gatsby</title>
    <author>F. Scott Fitzgerald</author>
    <year>1925</year>
  </book>
  <book id="b2">
    <title>To Kill a Mockingbird</title>
    <author>Harper Lee</author>
    <year>1960</year>
  </book>
</library>