ZUGFeRD / Factur-X
A hybrid e-invoice format combining a visual invoice with structured XML data. The amount of mandatory information and business rules depends on the selected profile.
Validate ZUGFeRD & Factur-X for free
Upload a PDF or XML invoice and validate ZUGFeRD / Factur-X and EN 16931 with Mustangproject.
ZUGFeRDFactur-XEN 16931PDF / XMLMustangproject 2.26.0
Create compliant e-invoices automatically
VersandFaktur creates invoices from eBay and Allegro orders and supports ZUGFeRD / Factur-X and KSeF workflows.
ZUGFeRD, Factur-X and EN 16931 explained
ZUGFeRD and Factur-X combine a human-readable invoice with structured XML invoice data. The recipient can view the invoice like a normal document while software can process the embedded data automatically.
EN 16931
The European semantic standard for electronic invoicing defines business terms, mandatory information, total relationships and rules for VAT calculations.
XRechnung
A German CIUS based on EN 16931. XRechnung is used as a structured XML invoice. Relevant profiles can be validated where supported by the Mustangproject version in use.
What does the free ZUGFeRD validator check?
The uploaded file is passed locally to Mustangproject on the VersandFaktur server. Depending on the file type and detected profile, several validation layers are evaluated:
- XML structure, schema and the validation rules applicable to the detected invoice profile.
- EN 16931 business rules, including relationships between net amount, VAT, gross amount and amount due.
- For PDFs, PDF/A properties plus relevant ZUGFeRD / Factur-X metadata and the embedded XML invoice.
- Detected profile and technical validator messages so errors can be corrected precisely.
Understanding common EN 16931 errors
Many invalid e-invoices fail because of mathematical relationships in the XML rather than the visible PDF. These rules are especially useful when troubleshooting:
The sum of invoice line net amounts does not match the document line total. Typical causes are rounding or a line changed after totals were calculated.
The invoice total excluding VAT does not match line totals, charges and allowances.
The invoice total including VAT does not match the total excluding VAT plus VAT.
The amount due does not consistently account for the invoice total, prepaid amounts or a rounding amount.
The VAT amount for a tax category does not match taxable amount × VAT rate after the required rounding.
One-cent differences on marketplace invoices
When a marketplace supplies an authoritative gross selling price, converting that amount back to net and VAT can create a one-cent difference. It should not be hidden by using an incorrect VAT amount. EN 16931 provides a rounding amount (BT-114) so correct tax math and the actual invoice amount can coexist.
Why PDF/A and embedded XML are separate checks
A valid XML file alone does not automatically make a hybrid ZUGFeRD / Factur-X PDF valid. For PDF invoices Mustangproject also checks PDF/A properties and relevant metadata, so the XML and PDF/A results can differ.
What does “valid” mean?
“Valid” means Mustangproject reported no failing technical validation rule for the uploaded file and detected profile. This is a technical validation and does not replace tax or legal review of the underlying business transaction.
How to handle a validation error
- Note the rule code such as BR-CO-17 and read the related message.
- Compare the affected amounts or mandatory fields in the XML with the visible invoice data.
- Validate the corrected invoice again, ideally before it is sent to the recipient.
ZUGFeRD validator FAQ
What is checked?
Mustangproject validates the embedded Factur-X/ZUGFeRD XML and, for PDF files, PDF/A properties as well. Depending on the profile, EN16931 rules are evaluated.
Are invoices stored?
No. The uploaded file is deleted from the private temporary directory after validation.
Which files are accepted?
PDF and XML files up to 10 MB. PDFs must have a real PDF signature; XML is parsed without external network resources.
Are ZUGFeRD and Factur-X the same?
The current generations of ZUGFeRD and Factur-X are closely harmonised. Depending on the file and profile, a German ZUGFeRD invoice can therefore contain a Factur-X profile identifier.
Is XRechnung the same as ZUGFeRD?
No. Both are based on EN 16931, but they are different implementations. XRechnung is a German CIUS used as structured XML; ZUGFeRD / Factur-X typically combines a visual invoice with embedded XML data.
What does BR-CO-17 mean?
BR-CO-17 concerns VAT calculation for a VAT category. The taxable amount and VAT rate must match the reported VAT amount according to EN 16931 rounding rules.
Can the XML be valid while the PDF validation fails?
Yes. XML rules and PDF/A properties are separate validation layers. A hybrid invoice can therefore pass XML validation while PDF/A or metadata still contains errors.