Unified read / write / stats / recalc / chart capability for Excel / CSV (.xlsx / .xlsm / .csv / .tsv). Trigger scenarios: reading cells, summarizing, grouping, highest/lowest values, total revenue, editing cell values or formulas, inserting rows/columns, adding total rows, inserting charts (bar/line/pie), freezing panes, auto-filter, conditional formatting, CSV ↔ XLSX conversion, building rosters / sales sheets / financial models, diagnosing #REF! / #DIV/0! formula errors, triggering recalculation. Typical phrasings: "who has the highest sales in this sheet", "total Q1 revenue", "change B2 to 500", "add a total row", "create a new roster", "convert csv to xlsx", "freeze the first row", "highlight negatives in column A red". Load this skill whenever the user mentions an .xlsx / .csv file or the final deliverable is a spreadsheet.