(From the JATS4R website)

JATS4R produces and makes available an online tool to validate an XML document both against the appropriate JATS DTD (NISO JATS version 1.0, 1.1 or 1.2), as well as against the JATS4R published recommendations.

The source code (MIT-licensed where applicable) is available for the JATS4R user interface, the validator web service, the Schematron rules, and the JATS DTDs.

When a user‘s XML content is sent to the JATS4R web service for validation, the doctype is logged, for usage metrics, but the rest of the XML document is not stored.