XSDHub
Check XML syntax, validate against XSD 1.0 (including multi-file schema projects) and format XML locally in your browser, no account needed. Every error guide comes with a broken and a corrected example you can open and test. Optional server checks add XSD 1.1, Schematron and e-invoice rules (EN 16931, XRechnung, Factur-X, KSeF, RO e-Factura, Croatia), only after explicit consent. Free for single files; Pro and Team add batches, saved schemas, an API and a GitHub Action.