I built Libreta because I was getting annoyed with how long it took Claude to do Excel work in the terminal, and how inconvenient it was to review in the Excel app. Plus it had issues running the formulas and no good way to get diffs. My thinking was to get spreadsheets to their plaintext essentials for agents to do the work, and set up an interface optimized for reviewing. Personal experience with Libreta so far has been pretty good, it's super fast and easier to audit. I've mostly tried it on basic models and personal spreadsheet work. Curious to see where this approach breaks down for others.