XML Mismatched Tag – Find Opening and Closing Tag Errors
A mismatched tag error means an element closes with a different name than the element currently open at that nesting level.
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XML Troubleshooting
Find XML well-formedness problems involving tags, attributes, entities, namespaces, declarations, CDATA, comments, and root structure.
Diagnostic workflow
How to troubleshoot XML problems
XML parsers stop on strict well-formedness rules, so begin at the first reported location and verify the surrounding element boundaries. A single missing quote, mismatched tag, or unescaped character can make later markup look broken even when those later elements are correct.
- Verify opening and closing tag names, nesting order, and the requirement for exactly one document root before checking application-specific XML rules.
- Inspect attributes for quotes, duplicate names, missing equals signs, and namespace prefixes that do not have an in-scope declaration.
- Check text and attribute values for raw ampersands, less-than signs, malformed character references, or unfinished CDATA and comment sections.
Browse focused fixes
Common XML problems
24 troubleshooting pages
XML Unclosed Tag – Find Missing Closing Tags
An unclosed tag leaves an element open when the parser reaches a parent boundary or the end of the XML document.
Read fixMultiple Root Elements in XML – Fix Extra Top-Level Elements
A well-formed XML document has exactly one document element, so two sibling top-level elements cannot both be roots.
Read fixUnescaped Ampersand in XML – Fix & Entity Errors
A bare ampersand starts XML entity-reference syntax, so ordinary text containing & must escape it as & unless a valid entity follows.
Read fixUnescaped Less-Than Sign in XML – Fix < in Text
A literal less-than sign cannot appear directly in XML character data because < begins markup such as an element, comment, or processing instruction.
Read fixDuplicate XML Attribute – Fix Repeated Attribute Names
An XML start tag cannot contain the same attribute name more than once, even when the duplicate values are identical.
Read fixUnquoted XML Attribute Value – Fix Missing Attribute Quotes
XML requires attribute values to be enclosed in matching single or double quotes, even when the value contains only letters or digits.
Read fixUnclosed XML Comment – Fix Missing --> Comment Endings
An XML comment starts with <!-- and must end with -->. Without that terminator, later markup remains inside an unfinished comment and the document cannot parse.
Read fixUndefined XML Entity – Fix Entity Not Defined Errors
An undefined entity error means the parser encountered a named entity reference that XML does not know in the current document.
Read fixXML Entity Missing Semicolon – Fix EntityRef Errors
XML entity references must end with a semicolon, so a sequence such as & followed by ordinary text is not a complete reference.
Read fixInvalid XML Character Reference – Fix Numeric Entity Errors
An invalid character reference points to a code point that XML cannot represent or that falls outside the valid Unicode range.
Read fixInvalid XML Element Name – Fix Start Tag Name Errors
XML element names must follow XML name syntax and cannot begin with characters such as ordinary digits.
Read fixUndeclared XML Namespace Prefix – Fix Prefix Not Defined Errors
A prefixed XML name such as x:item must have the prefix bound to a namespace URI in scope.
Read fixUnclosed XML CDATA Section – Fix Missing ]]> Errors
A CDATA section that starts with <![CDATA[ must end with ]]> before XML markup can resume.
Read fixDouble Hyphen in XML Comment – Fix Invalid -- Comment Syntax
XML comment content cannot contain the double-hyphen sequence --, even when the final --> terminator is present.
Read fixXML Declaration Not at Start – Fix Declaration Position Errors
When an XML declaration is present, it belongs at the beginning of the XML document rather than after the root element or ordinary content.
Read fixText Before XML Root Element – Fix Content Before the Root Tag
XML may contain prolog markup before the root element, but ordinary character data cannot appear there.
Read fixText After XML Root Element – Fix Trailing Content Errors
After the single document element closes, ordinary character data cannot continue as a second payload outside the XML tree.
Read fixXML Attribute Missing Equals Sign – Fix name"value" Syntax
Every XML attribute must use a name, an equals sign, and a quoted value.
Read fixUnescaped Quote in XML Attribute – Fix Broken Attribute Values
A quote matching the attribute delimiter ends the value, so the same quote cannot appear literally inside that value.
Read fixExtra Closing Tag in XML – Remove Unexpected End Tags
An extra closing tag appears when the parser encounters </name> but no matching element remains open at that position.
Read fixXML DOCTYPE After Root Element – Move DOCTYPE to the Prolog
A document type declaration belongs in the XML prolog before the root element, not in the epilog after it closes.
Read fixUnclosed XML Processing Instruction – Fix Missing ?> Terminators
A processing instruction that begins with <?target must end with ?> before normal XML markup continues.
Read fixCDATA End Marker ]]> in XML Text – Fix Invalid Character Data
The exact ]]> sequence is reserved as the end of a CDATA section and cannot appear literally in normal XML character data.
Read fixUnderstand the underlying concepts
XML guides
1 related guides
XML Parsing and Validation Errors Explained
Understand XML parsing and well-formedness errors, how to read parser messages, and how tags, entities, attributes, namespaces, and document structure cause validation failures.
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