XML Validator

Welcome to the XML Validator, a powerful online tool for checking whether your XML documents are well-formed. This validator instantly detects syntax errors, reports precise error locations, and provides document statistics to help you understand your XML structure. Whether you are a web developer, data analyst, or learning XML, this tool ensures your XML documents meet all fundamental syntax requirements.

What is Well-Formed XML?

A well-formed XML document follows all the basic syntax rules defined by the XML specification. Unlike valid XML (which must conform to a schema), well-formed XML simply needs to be parseable by any XML processor. Here are the key rules:

Features

• Instant Validation: Check XML well-formedness with one click
• Precise Error Reporting: Get exact line and column numbers for errors
• Error Highlighting: Jump directly to the problematic line in your code
• Document Statistics: View element counts, maximum depth, and attribute counts
• Structure Visualization: See your XML hierarchy in a tree view
• Code Formatting: Auto-format messy XML with proper indentation
• Quick Examples: Test with pre-built valid and invalid XML samples
• Iterative Correction: Fix one error at a time for easier debugging

How to Use This Tool

1. Enter Your XML: Paste your XML code into the editor, or click a quick example button to load sample data.
2. Optional Formatting: Click "Format" to auto-indent your XML for better readability.
3. Click Validate: Press the "Validate XML" button to check your document.
4. Review Results: If valid, you will see success confirmation with statistics. If there are errors, you will see the error message with line and column information.
5. Fix and Repeat: For errors, click "Jump to Error" to see the problematic line, make corrections in the editor above, and validate again.

Common XML Errors and Solutions

Mismatched Tags

This occurs when opening and closing tags do not match. Remember that XML is case-sensitive.

• Wrong: <Name>John</name>
• Correct: <Name>John</Name>

Unclosed Elements

Every opening tag must have a corresponding closing tag, or use self-closing syntax.

• Wrong: <item>Text
• Correct: <item>Text</item> or <item />

Unquoted Attributes

Unlike HTML, XML requires all attribute values to be quoted.

• Wrong: <book id=123>
• Correct: <book id="123">

Unescaped Special Characters

Characters like <, >, and & have special meaning and must be escaped.

• Wrong: <formula>x < 5</formula>
• Correct: <formula>x &lt; 5</formula>

XML Entity Reference Table

Frequently Asked Questions

What does it mean for XML to be well-formed?

Well-formed XML adheres to all XML syntax rules: it has exactly one root element, all tags are properly closed and nested, attribute values are quoted, element names are case-sensitive and follow naming rules, and special characters are properly escaped. A well-formed document can be parsed by any XML parser.

What is the difference between well-formed and valid XML?

Well-formed XML follows basic syntax rules and can be parsed. Valid XML is well-formed AND conforms to a specific schema (DTD or XSD) that defines allowed elements, attributes, and their relationships. This tool checks well-formedness. For schema validation, you need to specify a DTD or XSD.

Why do I get mismatched tag errors?

Mismatched tag errors occur when opening and closing tags do not match. Common causes include: typos in tag names (XML is case-sensitive, so <Name> and </name> do not match), forgetting to close a tag, or incorrectly nested tags. Always close tags in reverse order of opening.

How do I fix unexpected character errors?

Unexpected character errors usually mean special characters are not escaped. In XML, use &lt; for <, &gt; for >, &amp; for &, &apos; for ', and &quot; for ". Also check for invisible characters copied from word processors, and ensure the document uses valid encoding (UTF-8 recommended).

Can I validate XML with namespaces?

Yes, this validator handles XML with namespaces. Namespace declarations (xmlns attributes) are checked for proper syntax. However, this is a well-formedness checker, not a schema validator, so it verifies namespace syntax but not whether elements belong to the correct namespace as defined by a schema.

Additional Resources

• W3C XML Specification
• XML - Wikipedia