Introduction

pax.XRechnung.NET is a .NET library that helps validate, map, and generate XRechnung XML invoices, following specification 3.0.2.

Features

• ✅ Validation: Ensure XML invoices conform to XRechnung 3.0.2 schema and Schematron rules.
• 🔁 Mapping: Convert XML invoices into strongly typed DTOs.
• 🧾 Generation: Create compliant XML invoices from C# objects.

Getting started

Installation

dotnet add package pax.XRechnung.NET

Usage

Validate XML schema

    var xmlText = "<Invoice>...</invoice>";
    var serializer = new XmlSerializer(typeof(XmlInvoice));
    using var stream = new MemoryStream(Encoding.UTF8.GetBytes(xmlText));
    stream.Position = 0;
    var xmlInvoice = (XmlInvoice?)serializer.Deserialize(stream);
    Assert.IsNotNull(xmlInvoice);
    var validationResult = XmlInvoiceValidator.Validate(xmlInvoice);
    Assert.IsTrue(validationresult.IsValid);

Handle Sample Invoice

public static InvoiceBaseDto GetInvoiceBaseDto()
{
    return new()
    {
        GlobalTaxCategory = "S",
        GlobalTaxScheme = "VAT",
        GlobalTax = 19.0,
        Id = "1",
        IssueDate = new DateTime(2025, 05, 01),
        InvoiceTypeCode = "380",
        DocumentCurrencyCode = "EUR",
        SellerParty = new PartyBaseDto()
        {
            Name = "Seller Name",
            StreetName = "Test Street",
            City = "Test City",
            PostCode = "123456",
            CountryCode = "DE",
            Telefone = "1234/54321",
            Email = "seller@example.com",
            RegistrationName = "Seller Name",
            TaxId = "DE12345678"
        },
        BuyerParty = new PartyBaseDto()
        {
            Name = "Buyer Name",
            StreetName = "Test Street",
            City = "Test City",
            PostCode = "123456",
            CountryCode = "DE",
            Telefone = "1234/54321",
            Email = "buyer@example.com",
            RegistrationName = "Buyer Name",
            BuyerReference = "04011000-12345-34",
        },
        PaymentMeans = new PaymentMeansBaseDto()
        {
            Iban = "DE12 1234 1234 1234 1234 12",
            Bic = "BICABCDE",
            Name = "Bank Name",
            PaymentMeansTypeCode = "30",
        },
        PaymentTermsNote = "Zahlbar innerhalb von 14 Tagen nach Erhalt der Rechnung.",
        PayableAmount = 119.0,
        InvoiceLines = [
            new InvoiceLineBaseDto()
            {
                Id = "1",
                Quantity = 1.0,
                QuantityCode = "HUR",
                UnitPrice = 100.0,
                Name = "Test Job"
            }
        ]
    };
}

Serialize DTO to XML

    var invoiceBaseDto = GetInvoiceBaseDto();
    var mapper = new InvoiceMapper();
    var xmlInvoice = mapper.ToXml(invoiceBaseDto);
    var xmlText = XmlInvoiceWriter.Serialize(xmlInvoice);

Validate schema and Schematron locally (.NET and Blazor WASM)

    var invoiceBaseDto = GetInvoiceBaseDto();
    var mapper = new InvoiceMapper();
    XmlInvoice xmlInvoice = mapper.ToXml(invoiceBaseDto);
    var result = await XmlInvoiceValidator.ValidateSchematron(xmlInvoice);
    var resultText = string.Join(Environment.NewLine, result.Validations.Select(s => $"{s.RuleSeverity}:\t{s.Code}: {s.Message}"));
    Assert.IsTrue(result.IsValid, resultText);

The InvoiceBaseDto is designed to be easily extended see BaseDtoExtensionTests

ValidateSchematron now runs locally when no server URI is supplied. It supports standard XRechnung 3.0 UBL Invoice documents with customization ID urn:cen.eu:en16931:2017#compliant#urn:xeinkauf.de:kosit:xrechnung_3.0. The embedded rules are pinned to KoSIT configuration 2026-08-31, using EN 16931 1.3.16 and XRechnung Schematron 2.6.0. Extension, CVD, UBL CreditNote, CII, and other profiles require an external validator.

The validator uses The Saxon XSLT and XQuery Processor from Saxonica Limited (SaxonCS-HE 13.0.0). It works offline after application assets load and caches compiled stylesheets. Code, Path, and RuleSeverity preserve business-rule details. Warnings and information do not invalidate an invoice. Because XmlSeverityType has only Error and Warning, informational messages have Severity == Warning and RuleSeverity == "information". Processing failures set Error; ordinary rule failures appear in Validations. Local results have an empty HttpStatusCode.

Release-published, trimmed .NET 10 Blazor WASM was tested in Chromium, including validation with networking disabled. This is not a guarantee for all browsers or AOT builds. The measured cold validation took about 10.7 seconds, and cached validations about 100 ms, for the small test fixture on this machine. The validation executes on the calling thread, so cold compilation can block the browser UI. The probe's framework assets total 13.4 MB Brotli-compressed, compared with 2.5 MB for a minimal matching Blazor app. These are artifact sizes, not measured BeInX download sizes. See the reproducible browser probe.

For a consumer such as BeInX, invoke ValidateSchematron(invoice) even when the configured server URL is empty. If an external validator is configured, pass its URI explicitly:

var result = await XmlInvoiceValidator.ValidateSchematron(
    xmlInvoice,
    string.IsNullOrWhiteSpace(config.SchematronValidationUri)
        ? null
        : new Uri(config.SchematronValidationUri));

This library change does not modify BeInX's export flow. That flow currently skips Schematron validation when no server URL is configured.

ZUGFeRD XML validation (EN16931 / Comfort)

var xml = GetGeneratedCiiXml();
var result = ZugferdXmlValidator.Validate(xml);
if (!result.IsValid)
{
    var details = result.Error ?? string.Join(Environment.NewLine,
        result.Validations.Select(m => $"{m.Code}: {m.Message} ({m.Path})"));
    // Report the errors before passing this exact XML to PDF generation.
}

This API validates CII with guideline ID urn:cen.eu:en16931:2017 against ZUGFeRD 2.3.3 / Factur-X 1.07.3 EN16931. Other profiles and syntaxes are rejected. Validation checks the profile XSD first, then its compiled Schematron XSLT and code lists; it runs locally on .NET and Blazor WASM. Compiled resources are cached and each call uses its own validation state. Warnings do not reject invoices; processing failures set Error. No invoice data leaves the process.

All normative artifacts and the test fixture come directly from the official FeRD ZF233_EN_01.zip. Official filenames, relative paths, import paths, and bytes are preserved. The complete schema dependency closure and six embedded resource hashes are verified. See provenance and licenses and offline browser measurements.

This API validates the XML only. It does not certify the PDF carrier, upgrade an invoice writer, or apply XRechnung/Peppol CIUS rules to the Comfort profile.

Java Schematron Validator

External validation remains available through an explicit URI, or directly through InvoiceKositValidator.Validate(xmlText), whose default is still http://localhost:8080. It requires a running KoSIT validation server. Setup: XRechnung usage.

var result = await XmlInvoiceValidator.ValidateSchematron(
    xmlInvoice, new Uri("http://localhost:9090"));

The supplied URI must expose KoSIT's raw XML/HTML response; a JSON API wrapper requires its own client. Browser HTTP validation also requires the server to permit the application's origin through CORS.

Server start: java -jar .\validationtool-1.5.0-standalone.jar -s .\scenarios.xml -r ${PWD} -D

ChangeLog

v0.3.3

• Add local ZUGFeRD 2.3.3 / Factur-X 1.07.3 EN16931 (Comfort) XML validation using untouched official FeRD schemas, compiled XSLT, and code lists. Includes offline browser verification and pinned artifact hashes.

v0.3.2

• Update to dotnet 10

v0.3.1

• Breaking Changes
• Code Lists fix to receive meta information
• DTO rework to be more flexible and robust:
• PaymentMeansTypeCode to PaymentMeans
• BuyerReference to BuyerParty

v0.3.0

• Breaking Changes
• DTO rework to be more flexible and robust.
• InvoiceAnnotationDto now available with Required fields and CodeList validation

v0.2.0

• Breaking Changes
• Fixed/Renamed XmlInvoice properties and dependencies. All existing properties are now xml schema conform.
• Added Kosit schematron validation. See Java Schematron Validator
• Replaced all DTOs with InvoiceBaseDto

v0.1.0

• Breaking Changes
• Added FinancialInstitutionBranch to FinancialAccountType (XmlPaymentInstructions)
• Seller/Buyer cleanup and reference XmlParty
• Changed XmlAdditionalDocumentReference to XmlAdditionalDocumentReferences as list

v0.0.1

• Initial release
• Support for invoice validation and serialization
• Partial DTO implementation