I've found that all the top foundation models already understand spreadsheets very well, as well as all the functions, as well as all the common spreadsheet pro

I've found that all the top foundation models already understand spreadsheets very well, as well as all the functions, as well as all the common spreadsheet problems people run into using them. The Internet is chock full spreadsheet support forums and tutorials, and the foundation models have all been trained on this data. With not very much effort, one can explain to an LLM "here is a spreadsheet, formatted as..." which takes about 150 word tokens, and then not much more mental effort in your favorite language to translate an arbitrary spreadsheet into that format, and one gets a very capable LLM interface that can help explain complex arbitrary spreadsheets as well as generate them on request. I've got finance professionals and attorneys using a tool I wrote doing this to help them understand and debug complex spreadsheets given to them by peers and clients.