XML Validate — Free Online Tool

An XML validator checks whether XML is well-formed, catching mismatched tags, invalid nesting, unescaped characters, and malformed declarations. It is useful for debugging SOAP payloads, SAML assertions, XML configuration files, and legacy integrations. SWEDevTools: Prism validates locally in your browser so sensitive payloads do not need to be uploaded to online validators.

Features

• Well-formedness checking: Catches common XML failures: broken nesting, missing end tags, and invalid characters.
• Integration-friendly debugging: Useful for SOAP/SAML payloads and vendor XML where small errors are hard to spot.
• Local-first privacy: Validate internal payloads locally when XML contains IDs, tokens, or personal data.
• Clear error feedback: Developer-friendly messages help you pinpoint the tag or character that breaks parsing.

Frequently Asked Questions

What does 'well-formed XML' mean?

It means the document follows core XML syntax rules: one root element, properly nested tags, quoted attributes, and valid characters.

Is well-formedness the same as schema validation?

No. Schema validation (XSD/DTD) enforces structure and allowed elements. Well-formedness only checks XML syntax.

Why does an ampersand (&) break XML?

In text and attributes, & must be escaped as & unless it starts an entity reference.

Do namespaces need to resolve to real URLs?

Not for parsing. The namespace URI is an identifier; it does not need to be reachable, but the declaration must be valid.

Why do I see an error near the end of the document?

A missing closing tag earlier can throw off the parser and only surface later. Fix the first error and re-run.

Are CDATA sections safer than escaping?

CDATA can simplify embedding text, but it has edge cases (the sequence ]]> cannot appear inside).

Can I validate SOAP or SAML payloads here?

Yes. Paste the full XML. For best hygiene, remove secrets before sharing with others.

Does this tool prevent XXE vulnerabilities?

Validation is not a security sandbox. In production, configure parsers securely (disable external entity resolution) to mitigate XXE.

What happened to smalldev.tools?

smalldev.tools is no longer available. Prism by SWEDevTools offers the same developer tools and more, with offline support, pipeline chaining, and completely free usage — no signup required.

Is Prism a good alternative to freeformatter.com for XML?

Yes. Prism handles XML formatting, validation, and conversion entirely in your browser with no data uploads, no ads, and full offline capability. Plus you can chain XML tools together in pipelines.