Modern Javascript: https://learn.microsoft.com/en-us/office/dev/add-ins/excel/custom-functions-overview https://learn.microsoft.com/en-us/office/dev/add-ins/exc

Modern Javascript: https://learn.microsoft.com/en-us/office/dev/add-ins/excel/custom-functions-overview https://learn.microsoft.com/en-us/office/dev/add-ins/excel/c... For the "task pane", if you need one, you can use React or Angular, but I prefer to use Vue (or no front-end framework is fine too). For the backend logic, just straight up Node + webpack. You could probably do this better with Vite, but I think Microsoft's starter templates all use webpack. You end up distributing a manifest file that tells Excel which server your assets and API live at. Warning: hot reload and dev debugging is quite a pain on macOS.