What problem does it solve? Working with spreadsheet files programmatically often leads to broken formulas, hardcoded values that can't update, and Excel errors like #REF! or #DIV/0! that go unnoticed until delivery. This Skill provides a complete workflow for creating, editing, and analyzing .xlsx, .xlsm, .csv, and .tsv files while guaranteeing zero formula errors in the final deliverable. ## Core Features & Use Cases - Formula-First Spreadsheet Creation: Build dynamic Excel files with openpyxl where all calculations use native Excel formulas instead of hardcoded Python-computed values, keeping workbooks updateable. - Automated Formula Recalculation and Error Detection: Run the included recalc.py script to recalculate all formulas via LibreOffice and receive a JSON report pinpointing every #REF!, #DIV/0!, #VALUE!, or #N/A error by sheet and cell. - Financial Modeling Standards: Apply industry-standard color coding (blue inputs, black formulas, green cross-sheet links), number formatting rules, and assumption-cell conventions for professional financial models. - Use Case: A user asks to build a revenue projection model from messy CSV data. The Skill cleans the data with pandas, constructs the model with openpyxl using live formulas, recalculates with LibreOffice, and fixes any reported errors before delivery. ## Quick Start Use the xlsx skill to create a financial model spreadsheet from my sales data with formulas for totals and growth rates, then verify it has no formula errors.