EN 16931 UBL

Writes the European electronic invoice as UBL 2.1, the syntax Peppol carries and most of Europe reads.

Install

dependencies:
  en16931: ^0.1.2
  en16931_ubl: ^0.1.3

Write an invoice out

Build it with en16931, check it, then hand it over.

import 'package:en16931/en16931.dart';
import 'package:en16931_ubl/en16931_ubl.dart';

final invoice = Invoice.fromLines(
  number: '2026-0042',
  issueDate: DateTime(2026, 9, 13),
  seller: const Seller(
    name: 'COMAPPS SRL',
    vatIdentifier: 'BE0123456789',
    electronicAddress: Identifier('0123456789', scheme: Scheme.belgianEnterprise),
    address: Address(city: 'Bruxelles', postalCode: '1000', country: 'BE'),
  ),
  buyer: const Buyer(
    name: 'Client SA',
    electronicAddress: Identifier('0987654321', scheme: Scheme.belgianEnterprise),
    address: Address(city: 'Namur', postalCode: '5000', country: 'BE'),
  ),
  lines: [
    InvoiceLine.of(
      id: '1',
      item: const Item(name: 'Consulting'),
      quantity: 8,
      unitPrice: 150.00,
      vatRate: 21,
      unit: UnitCode.hour,
    ),
  ],
);

if (validate(invoice).isEmpty) {
  final xml = writeUbl(invoice);
}

Read one back

A supplier invoice goes the other way. What the document does not carry is left out rather than guessed, so validate tells you what the supplier got wrong instead of the reader hiding it.

final invoice = readUbl(xml);

for (final violation in validate(invoice)) {
  print(violation); // [BR-16] The invoice has no line (BG-25).
}

readUbl throws UblFormatException on three things only: text that is not XML, a root that is neither an Invoice nor a CreditNote, and a document with no issue date. Those leave nothing to report on. Everything else is read as far as it goes.

A document written beyond the standard is read as far as the standard goes, and no further. readUblReporting says what was left behind, which matters more than it sounds: an invoice whose lines carry lines of their own comes back with the parents only, still adds up, and passes.

final read = readUblReporting(xml);

for (final element in read.skipped) {
  print(element); // 56 x cac:SubInvoiceLine (a line under a line, which ...)
}

ublElementsBeyondTheModel names what is looked for. It is a short list on purpose: a narrow signal that is true beats a wide one that cries wolf over every element the reader is right to ignore.

Worth knowing up front

The elements come out in the order the UBL schema fixes, which is not the order the standard lists the terms in. A receiver validates against that schema before it reads a single business rule, so an invoice whose elements are out of order is not rejected on its content: it is not read at all.

A credit note goes out under the CreditNote root, with CreditNoteLine and CreditedQuantity. The type codes 381, 396 and 532 take that root, and isCreditNote says which.

Amounts are written with two decimals and the currency they are in. A unit price keeps the decimals it was given.

What it does not do

It does not decide what an invoice has to contain: that is the model's business, and validate from en16931 says whether it holds up. A network or a country puts its own rules on top of the standard, and those live in a profile package: en16931_peppol for Peppol BIS Billing and en16931_xrechnung for Germany. Delivery is a separate choice: the same document goes over Peppol, through a portal, or as an attachment.

License

Released under the MIT licence.