xllify

xllify is a packaging tool and runtime that allows functions written in Luau and Python to be used as high-performance custom functions in your Microsoft Excel workbooks. In a bizarre collision of 1990s style development (the Excel C SDK) and 2025 era AI, I’ve been experimenting with having a Claude agent write Excel custom functions for xllify! As Excel itself is now fat and 40 years old, it could be donning ill-fitting running gear and developing an irrational interest in coffee beans....

Back in August, I introduced xllify. This was a project I started when in-between contracts. I’ve since distilled my definition of xllify to: xllify is a packaging tool and runtime that allows functions written in Luau and Python to be used as high-performance custom functions in your Microsoft Excel workbooks. Go have a look! Things have evolved. As with all projects, I try to ruthlessly simplify and make things faster....

Excel is the original rapid application development tool. Developers can do unholy things to get the job done with no code, or perhaps with just a smattering of VBA. Long term, these solutions can end up brittle and hard to extend. Over the years there have been many approaches for extending Excel beyond formula soup and VBA. There is the excellent Excel-DNA, PyXLL, Microsoft’s own Office.js and Python support, among others....