We say this up front because it is true: there are one-off tools for it, there are invoicing programs for under 15 euros a month, and for invoices to the federal government there is a free portal. If all you need is a file format, you do not need construction software for it.
The hard part is different: that the quantities in that file are right, that they belong to the correct item in the correct contract, and that when someone asks you can show where each number came from. An invoicing program does not cover that path – it ends in your folder.





