If you’re porting some formulas from one language to another, “correct” can be defined as “gets the same answers as before.” Assuming you can run both easily, this is easy to write a property test for.

Sure, maybe that’s just building something that’s bug-for-bug compatible, but it’s something Claude can work with.

For starters, Python uses IEEE 754, and Excel uses IEEE 754 (with caveats). I wonder if that's being emulated.