Why and how

Mustang: because invoices simply need to get faster.

Mustang makes your software read, write and validate (e.g. re-calculate) machine readable invoices, orders, or delivery advices:

Machine-readable data speeds up invoice processing, makes it less error prone, is often requested by your customers and has become mandatory e.g. for german B2G invoices and
Italian (and soon French!) domestic B2B invoices (read more about electronic invoices).

Machine readability is achieved with formats such as Cross Industry Invoice (XML), XRechnung (per se not a format, details), or Factur-X/ZUGFeRD/Order-X (Cross Industry Invoice XML embedded into human readable PDF). Unlike for more complex exchange, called EDI (e.g. Peppol), those formats do not need to support additional protocols, gather extra address information or run custom servers.


Mustangproject is a open source Java (Jar or Maven) and .net library, command-line tool, and provides a server with a REST API. Mustangproject 2.11.0 was released on 22.05.2024 and supports ZUGFeRD 2.2.0, ZUGFeRD 1, Factur-X 1 as well as UN/CEFACT CII XRechnung 3.0.1.

News archive


  • Read, write and validate ZUGFeRD 2/Factur-X, ZUGFeRD 1 and XRechnung
  • Convert PDF/A1 to PDF/A3
  • Embeddable java library based on PDFbox
  • Permissive license (APL2, free for use in commercial and noncommercial applications)
  • The Mustangproject library
    • is available via Maven Central supporting Maven and Gradle
    • can be embedded in your Java software
  • Command line tool
    • Runs on Linux, Mac OS and Windows with JRE 1.8
    • Add ZUGFeRD XML to PDF
    • Extract ZUGFeRD XML from PDF
    • Convert CII to UBL
    • Migrate ZUGFeRD 1 to 2 (experimental)
    • Convert PDF/A-1 to PDF/A-3
    • Find out how many PDFs are ZUGFeRD
  • Mustang Server
    • Reads, writes and validates ZUGFeRD 2/Factur-X and XRechnung
    • Converts CII to UBL
    • is a OpenAPI/Swagger REST API and uses oAuth
    • Phive-Validation of other formats and UBL
    • Converts any PDF to PDF/A-3

A Mustang Library .net Version is currently in Beta.

Screenshot of Acrobat Adobe PDF Reader showing a ZUGFeRD invoice with open file attachments tab
At the right you see a sample
PDF containing Factur-X/ZUGFeRD metadata generated with the Mustang library. If you open it in Adobe Acrobat Reader just click on the paperclip symbol to see the embedded ZUGFeRD XML structure. It has been created using the invoice class. Which you can also use to create a XRechnung.