Mustangproject is a tool to write, validate and parse Factur-X/ZUGFeRD and (CII)XRechnung e-invoices. It is a (permissive) open source cross platform command line tool and a Java library. The command line tool e.g. allows to extract and combine PDF and XML from/to Factur-X as well as validate e-invoices, convert XML to HTML or migrate from ZUGFeRD v1 to v2. The library additionally allows to generate the XML to be embedded either by implementing interfaces or actively creating objects.