XML Validator
Check if your XML is well-formed and valid. Get instant feedback with detailed error messages and line numbers.
XML Input
Runs fully in your browser. No data sent to our servers.
How to Validate XML
Paste or upload XML
Enter your XML content in the input area or upload an XML file from your computer.
Click Validate
Press the Validate button to check your XML for syntax errors and well-formedness.
Review results
See instant validation results. If errors are found, you'll get detailed messages with line numbers.
Fix and revalidate
Correct any errors using the provided guidance, then validate again until your XML passes.
Understanding XML Validation
Well-Formed vs Valid XML
There are two levels of XML correctness that developers need to understand:
Well-Formed XML
Follows basic XML syntax rules. Every XML document must be well-formed to be processed by any XML parser. This tool checks for well-formedness.
Valid XML
Well-formed AND conforms to a specific schema (XSD or DTD). Validation ensures your XML follows a predefined structure with correct elements and data types.
XML Well-Formedness Rules
For an XML document to be well-formed, it must satisfy these rules:
- ✓Exactly one root element contains all content
- ✓Every opening tag has a matching closing tag
- ✓Elements are properly nested (no overlapping)
- ✓Tag names are case-sensitive and must match
- ✓Attribute values are enclosed in quotes
- ✓Special characters are properly escaped
Common XML Errors and How to Fix Them
Mismatched Tags
❌ Invalid:
<Name>John Smith</name>✅ Valid:
<Name>John Smith</Name>Fix: XML is case-sensitive. Ensure opening and closing tags match exactly.
Improper Nesting
❌ Invalid:
<b><i>Bold and italic</b></i>✅ Valid:
<b><i>Bold and italic</i></b>Fix: Close inner tags before outer tags. Elements cannot overlap.
Unquoted Attribute Values
❌ Invalid:
<book category=fiction>✅ Valid:
<book category="fiction">Fix: Always enclose attribute values in double or single quotes.
Unescaped Special Characters
❌ Invalid:
<formula>5 < 10 & 10 > 5</formula>✅ Valid:
<formula>5 < 10 & 10 > 5</formula>Fix: Use XML entities: < for <, > for >, & for &
Multiple Root Elements
❌ Invalid:
<book>...</book>
<book>...</book>✅ Valid:
<library>
<book>...</book>
<book>...</book>
</library>Fix: Wrap all content in a single root element.
XML Entity Reference
These predefined entities must be used to represent special characters in XML content:
| Character | Entity | Numeric | Description |
|---|---|---|---|
| < | < | < | Less than (starts tags) |
| > | > | > | Greater than (ends tags) |
| & | & | & | Ampersand (starts entities) |
| " | " | " | Double quote (in attributes) |
| ' | ' | ' | Single quote (in attributes) |