Also called XRechnung 3.0, XRechnung CIUS
XRechnung is the German CIUS, a national specification that narrows EN 16931 by making some optional fields mandatory and forbidding some values the European standard allows. It is pure XML rather than a PDF, and it is what German public sector buyers require.
This is the single most common way a company believes it is compliant and is not. XRechnung requires fields EN 16931 leaves optional, most visibly the buyer reference (BT-10), and constrains values the European standard permits.
So a file can validate cleanly against EN 16931 and be rejected by a German buyer. If your validation tool only reports EN 16931 findings, it is not answering the question that buyer is asking.
Our validator keeps these separate on purpose. The EN 16931 rules run in your browser; the XRechnung rule set runs on our backend as an opt in. Until you run it, the report says the result is incomplete rather than telling you it passed.
Unlike Factur-X and ZUGFeRD, an XRechnung is a standalone XML file with no PDF wrapper. That is clean for the receiving software and unreadable for the person in accounts payable, which is exactly the tradeoff Factur-X was designed to avoid.
ZUGFeRD defines an XRECHNUNG profile, which is how you get an XRechnung conformant payload inside a PDF/A-3 container. If a German buyer accepts that, you get both properties at once.
XRechnung accepts both CII and UBL syntaxes, which is worth knowing before you assume the CII path you built for Factur-X covers it.
A separate opt in from the browser side EN 16931 check, because those rules need a server. A clean EN 16931 result never quietly claims XRechnung conformance.
