Back when starting our consulting company, we deemed invoicing a solved problem: Simply write them using office software, print to PDF, done. That solution did not make us happy, though. 

There was data redundancy in the various spreadsheets that we used to manage our company, plus concurrency and scalability issues due to binary file formats that you cannot easily diff. So we decided to build our own solution. After all, writing and managing invoices the way we need cannot be that hard – or so we thought. 

This is the story of how we went through iterations and rewrites, and what we have learned along he way. Well, we certainly learned to better understand some of the advice we give to our clients.