XML Validator Online
The XML validator confirms that a document is well-formed and, when it is not, reports the parser error with its position. It also summarises the document: root element, element count and maximum nesting depth.
XML to validate
Validation result
Your result will appear here.
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Runs in your browser. Processing happens entirely in your browser. Nothing you enter is sent to Delimiter.live.
How to use the XML Validator
- Paste the XML document you want to check.
- A valid document returns a structure summary; an invalid one returns the parser error and its position.
- Fix the reported problem and validate again.
Example
Input
<a><b></a>
Output
Not well-formed Mismatched tag: expected </b> but found </a>.
Common XML syntax errors and how to fix them
Nearly every well-formedness error is one of these. The validator reports the first one it meets, with its position.
| Example | Problem | Fix |
|---|---|---|
| <title>Hello | Unclosed tag | Close every element, <title>Hello</title>, or self-close an empty one as <br/> |
| <b><i>x</b></i> | Tags closed in the wrong order | Close elements in the reverse order they were opened |
| Fish & Chips | Unescaped ampersand | Write &, or wrap the text in a CDATA section |
| a < b | Unescaped less-than sign in text | Write < |
| <item id=5> | Unquoted attribute value | Quote every attribute value: id="5" |
| <a x="1" x="2"> | Duplicate attribute | Each attribute name may appear once per element |
| <a/><b/> | More than one root element | Wrap everything in a single root element |
| <Item></item> | Tag names that differ in case | Names are case-sensitive, so match them exactly |
| | An HTML entity XML does not define | XML has only & < > " ' — use   instead |
| <1st> | Name starting with a digit | Element names must start with a letter or underscore |
| ␣<?xml …?> | Something before the XML declaration | The declaration must be the very first thing in the file — no space or blank line before it |
Common use cases
- Finding the unclosed tag in a document a parser rejected.
- Checking a generated feed before publishing it.
- Confirming an SVG or configuration file is well-formed after editing.
- Checking a sitemap.xml or RSS feed before submitting it, since a feed that is not well-formed is rejected outright.
Limitations and things to watch for
- This checks well-formedness only — that tags are balanced, attributes are quoted and the document has a single root. It does not validate against a DTD, XSD or RelaxNG schema.
- Browser parsers report the first error and stop, so fixing one problem may reveal another.
Frequently asked questions
What does "well-formed" mean?
That the document follows XML syntax rules: one root element, every tag closed and correctly nested, attributes quoted, and reserved characters escaped. It is a lower bar than schema validity.
Can it validate against my XSD schema?
No. Schema validation needs the schema itself and a validating processor, which is beyond what a browser tool can do reliably. This tool checks well-formedness only.
Why does it only show one error?
Once an XML parser hits a structural error it can no longer trust the rest of the document, so it stops. Fix the reported error and run it again.
What is the difference between well-formed and valid XML?
Well-formed means the document follows XML syntax. Valid means it also conforms to a schema — a DTD or XSD that says which elements may appear where. Every valid document is well-formed, but not the reverse. This tool checks well-formedness.
Does it check sitemaps, RSS feeds and SVG files?
It checks that they are well-formed XML, which is the most common reason they fail. It does not check that they follow the sitemap, RSS or SVG specification — a feed can be perfect XML and still be missing a required element.