Mustangproject e-Invoicing Library

Mustangproject is a prominent open-source Java library and toolset designed to facilitate the creation, reading, and validation of electronic invoices, particularly those following the Factur-X and ZUGFeRD standards. Originally developed in Germany, it has become a critical component for developers needing to comply with European e-invoicing mandates, such as the EN16931 standard.

The project was established by Jochen Stärk and is maintained by Usegroup, based in Frankfurt. It provides a bridge between traditional PDF documents and structured XML data, allowing businesses to exchange human-readable documents that also contain machine-readable information. As an open-source initiative, its development is collaborative, though its primary stewardship remains in Germany.