XML Validator

Validate, format, and visualize XML data

Common XML Errors & How to Fix Them

Learn about common XML validation errors and how to fix them.

Error TypeDescription & SolutionCode Example

Mismatched Closing Tag

The closing tag does not match the opening tag. In XML, every opening tag must have a corresponding closing tag with the exact same name.

Common causes:
  • Typos in tag names
  • Copy-pasting errors
  • Case sensitivity mismatch (XML is case-sensitive)
How to fix:
  1. Check the spelling of both opening and closing tags
  2. Ensure case matches exactly (e.g., <User> and </user> is invalid)
  3. Use an editor with tag matching to highlight pairs
Incorrect
Correct

Missing Closing Tag

An opening tag is present but the closing tag is missing.

Common causes:
  • Forgetting to close a tag
  • Nesting errors where a parent tag is closed before its children
  • Self-closing tag syntax errors
How to fix:
  1. Locate the unclosed element
  2. Add the closing tag (</tagname>) at the appropriate position
  3. Use self-closing syntax (<tag />) for empty elements
Incorrect
Correct

Unquoted Attribute Values

Attribute values must always be quoted in XML. Unlike HTML, XML is strict about quotes.

Common causes:
  • HTML habits (HTML often allows unquoted attributes)
  • Lazy typing
  • Generating XML via partial string concatenation
How to fix:
  1. Wrap all attribute values in double quotes (") or single quotes (')
  2. Example: page="1" instead of page=1
Incorrect
Correct

Improper Nesting

Tags are not nested correctly. A tag opened inside another tag must be closed before the outer tag is closed.

Common causes:
  • Confusing the order of closing tags
  • Editing large blocks of XML
How to fix:
  1. Follow the LIFO (Last In, First Out) rule for tags
  2. Close the specific inner element before closing the outer wrapper
Incorrect
Correct

Multiple Root Elements

An XML document must have exactly one root element that contains all other elements.

Common causes:
  • Concatenating two XML files
  • Forgetting a wrapper element
  • Fragments of XML data
How to fix:
  1. Wrap your elements in a single parent element (e.g., <root> or <data>)
  2. Ensure the declaration <?xml ...?> is at the very top, followed by one root tag
Incorrect
Correct

Unescaped Special Characters

Using special characters like <, >, &, ", or ' directly in text or attributes without escaping them.

Common causes:
  • Pasting raw text content
  • URLs containing ampersands (&)
  • Mathematical formulas (< or >)
How to fix:
  1. Replace < with &lt;
  2. Replace > with &gt;
  3. Replace & with &amp;
  4. Replace " with &quot;
  5. Replace ' with &apos;
  6. Or wrap content in a CDATA section: <![CDATA[5 < 10]]>
Incorrect
Correct

Related Resources

Convert XML to JSON

Use our tool to transform your XML data into JSON format efficiently.

Features

  • Validate XML syntax in real time
  • Auto-format and beautify XML with "Repair" button
  • Visualize XML structure as an interactive tree
  • Highlight errors with line numbers
  • Detect invalid nesting and missing tags

How to Validate XML

  1. Paste your XML into the editor.
  2. Click Validate XML to check for errors.
  3. Click Repair / Format to beautify the code.
  4. Click Visualize to explore the data structure.