Validating e-invoices: How to check XRechnung & ZUGFeRD for free
Whether an e-invoice is truly standards-compliant only becomes clear through validation against EN 16931. How to check invoices for free and fix typical errors.
Why "looks fine" is not enough
An e-invoice is only legally compliant if its structured data set conforms to the European standard EN 16931 — and that cannot be seen from a PDF view. A ZUGFeRD document can look visually flawless and still contain faulty or incomplete XML. Recipient systems check automatically: if the invoice fails validation, it is rejected and payment is delayed.
What validation checks
- Schema validation: is the XML technically well-formed and does it conform to the syntax (UBL or UN/CEFACT CII)?
- EN 16931 business rules: are all mandatory fields (business terms) present and consistent — such as invoice number, tax rates, and totals?
- National rules: additional German requirements apply to XRechnung (CIUS XRechnung), such as the mandatory Leitweg-ID for invoices to public authorities
- Arithmetic check: do line totals, tax amounts, and the gross amount add up correctly?
Free validation tools
For a quick practical test, the free online validator from taxlayer is well suited: upload an XRechnung or ZUGFeRD file, and you receive an understandable analysis of standard and rule violations. Technically experienced teams can additionally use the reference tools from KoSIT (validator with XRechnung scenarios), though their reports require some familiarization. Important: do not validate just once, but after every software update and every format change.
The most common validation errors and their causes
- Missing mandatory information: buyer reference, payment terms, or contact details are not maintained in the invoicing system
- Wrong tax categories: tax-exempt transactions without the corresponding exemption reason code
- Rounding differences: line amounts and totals deviate by cent amounts because the upstream system rounds differently
- Outdated profiles: ZUGFeRD 1.0 or the BASIC-WL profile do not meet the requirements of EN 16931
- Invalid identifiers: faulty VAT ID, IBAN, or Leitweg-ID in the master data
From error report to clean invoice
Most validation errors are master data errors: corrected once in the ERP or invoicing system, they disappear from all subsequent invoices. Therefore, always fix errors at the source rather than in the individual document. If your system does not generate standards-compliant data at all, services such as taxlayer.de convert existing PDF invoices into valid ZUGFeRD or XRechnung files. Which format fits which recipient is explained in the comparison ZUGFeRD vs. XRechnung.
Frequently asked questions
Is an invoice invalid if the validator shows warnings?
No. Validators distinguish between errors (violations of mandatory rules — the invoice is not standards-compliant) and warnings (notes on recommended but not mandatory information). Errors must be fixed; warnings should be reviewed, but they do not make the invoice impermissible.
Do I also have to validate incoming e-invoices?
It is strongly recommended. As the recipient, you bear the input VAT deduction risk: if mandatory information under § 14 para. 4 UStG is missing, the tax office can deny the deduction. An automated inbound check detects faulty invoices immediately, so you can request a correction from the supplier before anything is posted and paid.
What is the difference between a schema check and a Schematron check?
The schema check ensures the XML is syntactically correct — the right elements in the right place. The Schematron check then applies the substantive business rules of EN 16931 and national requirements, such as calculation rules and dependencies between fields. A standards-compliant e-invoice must pass both check levels.
How do I check whether my ZUGFeRD PDF contains XML at all?
Open the file in a PDF reader with an attachments view: the XML is visible as an embedded file (usually factur-x.xml or xrechnung.xml). If the attachment is missing, it is a simple PDF without structured data — and thus, from the statutory deadlines onward, no longer an e-invoice within the meaning of § 14 UStG. An online validator will also show you this immediately.
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