Free Online XML Validator
XML Validator helps you check any XML document for well-formedness errors, structural issues, and best practice violations right in your browser. We built five XML analysis utilities into one workspace so you can validate syntax, analyze structure, lint for code quality, check namespace declarations, and verify encoding without installing software or creating an account. Paste your XML, upload a file, and get a detailed validation report in seconds. Your data never leaves your device.
XML Validator
Checks XML well-formedness for unclosed tags, mismatched elements, unescaped characters, and missing declaration attributes. Reports each issue with severity and line number.
XML Structure Analyzer
Parses your document and reports element counts, attribute totals, text nodes, nesting depth, unique tag names, and the most frequently used elements.
XML Lint
Scans for best practice violations including mixed naming conventions, empty elements, empty attributes, extra whitespace, and non-standard boolean values.
Namespace Check
Validates namespace declarations by detecting undeclared prefixes, unused namespaces, and empty URIs across your XML document.
Encoding Check
Analyzes encoding declarations, detects non-ASCII characters, counts numeric entities, and warns about Byte Order Marks that may cause parser issues.
Online XML Validator with Detailed Error Reporting
Broken XML causes silent failures in production. A single unclosed tag, a mismatched element name, or an unescaped ampersand can bring down an entire data pipeline. Our online XML validator catches these problems before they reach your users. You paste or upload your XML, and the validator scans for every well-formedness violation in real time. Each issue appears in a structured report with a severity badge, the exact line number, and a plain-language description of what went wrong and where to look.
What the Validator Checks
The well-formedness checker tracks opening and closing tags through a stack-based algorithm. When it finds a closing tag that does not match the most recent opening tag, it reports the mismatch with both line numbers so you can trace the problem. Orphan closing tags with no matching opener get flagged separately. The validator also scans for unescaped ampersands that break parsers and verifies that the XML declaration includes the required version attribute. A summary bar at the top of the results panel shows error, warning, and info counts at a glance, followed by a color-coded status strip that tells you instantly whether your XML passed or failed.
Upload XML Files Directly
You can drag and drop files directly onto the editor or click the Upload XML button. We accept .xml, .xsl, .xslt, .svg, .xhtml, .rss, and .atom files. Because everything runs locally in your browser, there is no upload limit and no risk of exposing database credentials, internal endpoints, or customer data to external servers.
Analyze, Lint, and Inspect Your XML
Beyond basic validation, we provide four additional analysis tools that help you understand and improve your XML documents. The Structure Analyzer parses your document with the browser DOMParser and reports element counts, attribute totals, nesting depth, and the most frequently used tag names. If your nesting exceeds 10 levels, a warning appears suggesting you consider flattening for better readability.
The XML Lint tool scans for best practice violations that parsers accept but humans struggle with. It detects mixed naming conventions where some tags use camelCase and others use snake_case. It flags empty elements that could be self-closing, empty attribute values, and extra whitespace around attribute equals signs. Missing XML declarations and non-standard boolean values like "yes" or "0" instead of "true" or "false" are reported as informational notes so you can decide whether to fix them.
Namespace and Encoding Validation
SOAP messages, RSS feeds, and enterprise XML documents rely heavily on namespaces. Our Namespace Check tool lists every xmlns declaration with its prefix and URI, then cross-references those declarations against actual prefix usage in the document. Prefixes that are used without a matching declaration are flagged as errors. Declared namespaces that are never referenced anywhere get warning flags. Empty namespace URIs are also caught.
The Encoding Check tool reads the XML declaration for encoding information, scans for non-ASCII characters and reports their locations, counts numeric and hexadecimal character entities, and compares byte size against character count to detect multi-byte encoding. A Byte Order Mark at the start of the file triggers a warning since some XML parsers choke on BOM characters.
Your Data Stays on Your Device
We process everything in your browser using the built-in DOMParser API and JavaScript string operations. Your XML never touches our servers. That means you can safely validate production configs with database credentials, SOAP definitions with internal endpoints, and data feeds with customer information. No server communication, no cookies, no signup required.
Related XML and Data Tools
If you work with XML regularly, these free tools complement what you can do here:
- XML Optimizer -- optimize XML with configurable passes for size reduction
- XML Pretty Print -- pretty print XML with configurable indentation
- XML Minifier -- minify XML with comment and whitespace removal
- XPath Tester -- test XPath expressions against XML documents
- JSON Formatter -- format, minify, validate, and transform JSON data
- HTML Minify -- minify, expand, validate, and transform HTML code
- Code Formatter -- format HTML, CSS, JSON, XML, and JavaScript in one tool