How you can help


If you are a developer and you know what to work on we are happy to assist. If you don't know what to work on, or where to start, or if you want to improve your development skills, please feel free to apply for a open source mentorship. If you can't develop you can still


When we change Mustangproject we usually run the automatic tests and run two validators on the output to see if it remains valid, the Other validators include VeraPDF (PDF only) and Konik (XML only).

Internal architecture

We need money for a booth on the annual ZUGFeRD conference and for the development of our opensource ZUGFeRD validator.


ZUV (ZUgferd and VeraPDF) is a ZUGFeRD Validator, released into public beta on 27 April 2018.

It's a command line tool but FerdMC published a online version on their ZUGFeRD community page.

It will be integrated into Mustangproject in 2018 and checks PDF/A-3 compliance (based on VeraPDF) and ZUGFeRD XML correctness. The XML is checked with the official ZUGFeRD version 1 schematron respectively with the EN16931 UN/CEFACT SCRDM v16B uncoupled schematron from CEN for the EN16931 profile of ZUGFeRD 2 public preview only.

There are better validators, but the only open source alternative did e.g. not check PDF correctness or ZUGFeRD 2 (public preview).


Corpus is a (Mustangproject-indendent) collection of freely accessible ZUGFeRD files, some of them found in the wild, some of them crafted. It contains valid and accidentally invalid ZF1 and ZF2/Factur-X files files in different profiles as well as specially crafted invalid files.


Feel free to submit files, in particular if you are using a ZUGFeRD engine which is not yet listed.

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