Klarfakt

Klarfakt is a .NET library for reading and validating EN 16931 electronic invoices without leaving your own process or relying on Java or Node. It runs the publishers' own compiled Schematron artefacts, fetched from pinned upstream releases and verified by SHA-256, rather than reimplementing rules. It supports UBL 2.1, CII D16B, and hybrid Factur-X/ZUGFeRD PDFs, and validates against EN 16931, Peppol BIS Billing 3.0, and XRechnung 3.0.2 rule sets. It can also render KoSIT's official XRechnung visualisation as a self-contained HTML page. The project targets developers building invoicing software, particularly relevant since German companies must now be able to receive electronic invoices. It is distributed as a NuGet package supporting net8.0 and net10.0.