E-invoice formats explained
Most of the confusing names describe the same thing: an invoice that follows the European standard EN 16931, written in one of two XML syntaxes.
UBL 2.1
An XML syntax from OASIS, used by Peppol and by many national rules. The file starts with <Invoice> or <CreditNote>.
UN/CEFACT CII
The second XML syntax allowed by EN 16931, from UN/CEFACT. The file starts with <CrossIndustryInvoice>. It is the XML inside ZUGFeRD and Factur-X.
XRechnung
The German profile of EN 16931. It can be written in UBL or in CII and adds German rules, for example the Leitweg-ID in the buyer reference for public bodies.
ZUGFeRD / Factur-X
One standard with a German and a French name. A PDF/A-3 file for people with a CII XML attached for software. The XML is the part that counts.
Peppol BIS Billing 3.0
The UBL profile used on the Peppol network. Mandatory for domestic B2B in Belgium and, from 2027, in Slovakia. Sender and receiver are identified by Peppol IDs.
e-SLOG 2.0
The Slovenian standard, used with public bodies and banks. It is an XML form of the EDIFACT INVOIC message; version 2.0 is aligned with EN 16931.
FatturaPA · KSeF FA(3) · Facturae
Italy, Poland and Spain use their own formats through national platforms. They are neither UBL nor CII, although the content is similar.
How to tell which one you have
Open the file in the Zaamm viewer: the format and the specification identifier are shown on the invoice. As a rule of thumb, a PDF is ZUGFeRD or Factur-X, an XML that starts with <Invoice> is UBL and one that starts with <CrossIndustryInvoice> is CII.