Xlsx

This gives Claude real spreadsheet capabilities through openpyxl and pandas, with an emphasis on producing zero-error Excel files that financial analysts would actually use. The documentation is thorough on formula construction (use cell references, not hardcoded values), color coding standards for financial models (blue for inputs, black for formulas, green for internal links), and number formatting conventions. It includes a recalc.py script that uses LibreOffice to calculate formula values and scan for errors, which is critical since openpyxl writes formulas as strings. The requirements section reads like it was written by someone who's debugged too many broken spreadsheets. If you're building financial models or data analysis tools where formulas need to work correctly and follow industry conventions, this is built for that exact use case.