E-Invoice Validator
Drop in a ZUGFeRD/Factur-X PDF or a raw XRechnung/UBL XML file and check it against the EN 16931 Schematron rules — the same check Invonio runs before sending a real invoice.
Why this exists
The same check we run before sending a real invoice
EN 16931 compliance isn't just well-formed XML — the Schematron rules catch rounding and business-rule mistakes no generator library prevents on its own.