Debugging a SOAP or SAML payload
Enterprise integrations fail on unescaped ampersands inside attribute values more often than on anything conceptually difficult. Validation points at the exact offset.
Developer🔒 Browser (client-side)API: browser-only📴 Works offlinebeginner
XML Validator
Validates XML syntax using the browser's built-in DOMParser.
Data stays in your browser
Ready to runInstant execution
Result
—What does this tool do?
Validates XML syntax using the browser's built-in DOMParser.
Why would I use it?
- An XML feed or config is rejected by a consumer and you need the error.
- You want to confirm well-formedness before transforming.
- You prefer a private check — the document never leaves your browser.
Real-life example
Input
<root><item>1</item></root>
Output
Valid XML ✓
Well-formed documents pass; malformed ones report a parser error.
Input → Process → Output → Next
- Input
- Paste XML.
- Process
- The browser's DOMParser attempts to parse it.
- Output
- Valid, or the parser error message with location.
- Next action
- Fix the reported tag mismatch or illegal character.
Common mistakes
- Unclosed tags or mismatched closing tags.
- Using undeclared entities like without a DTD.
- Multiple root elements — XML allows exactly one.
What the result means
Valid means well-formed XML; it does not validate against a schema (DTD/XSD).
Privacy & security
Your input is processed entirely in your browser and never sent to a YAS server.
API automation is not supported for this tool. Uses the browser DOMParser — no server XML parser is bundled by design. This tool intentionally cannot be executed through the YAS API (server-side).
API
No public API for this tool
This tool runs in your browser and cannot be executed through the YAS API. Uses the browser DOMParser — no server XML parser is bundled by design.
XML Validator: technical reference, use cases and FAQ
How XML Validator works
The document is parsed with the browser's built-in DOMParser in XML mode, which enforces well-formedness as defined by the XML 1.0 specification: exactly one root element, every start tag matched by an end tag in the correct nesting order, attribute values quoted, entities either predefined or declared, and reserved characters escaped. A parser error produces a parsererror element whose message carries the line and column.
Well-formedness is not validity in the XML sense. A well-formed document obeys the grammar; a valid document additionally conforms to a DTD or XML Schema that defines which elements may appear where, in what order and with what content types. This tool checks the first, which is what almost every 'invalid XML' error in practice turns out to be.
When to use it: real-world scenarios
Checking a hand-edited configuration file
Maven POMs, Android manifests, Spring contexts and .csproj files break builds with unhelpful errors when a tag is left unclosed.
Verifying a generated feed or sitemap
RSS, Atom and XML sitemaps must be well-formed before a consumer will read them. The Sitemap Validator adds sitemap-specific schema checks on top.
Inspecting XML pasted from a log or ticket
Copy-paste through chat and issue trackers introduces smart quotes and stripped escapes; validation identifies the damage immediately.
Pro tips
- Escape the five predefined entities in text and attribute values: & as &, < as <, > as >, " as " and ' as '. A bare ampersand is the single most common cause of malformed XML.
- Use CDATA sections for blocks containing markup or many special characters, but remember CDATA cannot contain the sequence ]]>.
- XML is case-sensitive: <Item> and <item> are different elements, and a mismatched pair is a well-formedness error, not a warning.
- Declare the encoding in the XML declaration and make sure the file is actually saved in that encoding — a mismatch produces errors at the first non-ASCII byte.
Limitations and edge cases
What this tool deliberately does not do, and where it will disagree with other implementations.
- Well-formedness only. No DTD, XSD or RELAX NG validation, so structural conformance to a schema is not checked.
- External entities are not resolved, deliberately — resolving them is the XXE vulnerability class.
- Namespace declarations are parsed but namespace-correctness (prefixes bound to the expected URIs) is not enforced.
- Browser-only, with no API endpoint, and bounded by available memory for very large documents.
Frequently asked questions
- What is the difference between well-formed and valid XML?
- Well-formed means it obeys XML syntax — matched tags, one root, escaped entities. Valid means it also conforms to a declared DTD or schema. This tool checks well-formedness, which covers the vast majority of real failures.
- Why does my ampersand break the document?
- In XML, & begins an entity reference. A literal ampersand must be written & anywhere it appears in text or an attribute value, including inside URLs.
- Can I validate against an XSD here?
- No. Schema validation needs the schema document and a validating processor; browsers do not ship one. Use xmllint or a language-specific validator for that step.
- Does it check my sitemap or RSS feed specifically?
- It checks that they parse. For sitemap-specific rules — element order, URL count and size limits — use the XML Sitemap Validator.
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