Nearly 4 years ago I wrote a library in Go to read XLSX - that was trivial. It's grown over time, and this year it started growing feature that allow it to write XLSX format. This is a whole different ball game - Microsoft Excel is really picky about what it will and won't accept. In most cases Excel will simply moan and do an automated repair on files that don't match exactly it's expectation. LibreOffice is less annoying in its XLSX handling.