XLSX Skill

Anthropic's official spreadsheet handler for Claude. It opens, builds, and edits Excel and CSV files — .xlsx, .xlsm, .csv, and .tsv — preserving formulas, formatting, and charts rather than flattening everything to plain values. It's aimed at anyone who hands Claude a real workbook and expects a real workbook back: analysts cleaning exports, ops folks maintaining trackers, and developers generating reports as part of a pipeline.

When to use it

• You have a messy export (misplaced headers, blank rows, mixed types) and want a clean, properly typed sheet.
• You need to add a computed column, a SUMIFS, or a pivot-style summary to an existing model without breaking its formulas.
• You want to turn a CSV into a formatted .xlsx with frozen headers, number formats, and a chart.
• You're converting between tabular formats (CSV ↔ XLSX, sheet → TSV).
• You need to read values out of a workbook to summarize or feed elsewhere.

How it works

Under the hood the skill drives the Python openpyxl library for cell-level work — styles, fonts, fills, number_format, merged cells, frozen panes, conditional formatting, and native chart objects (BarChart, LineChart, PieChart) added via ws.add_chart(). For bulk data wrangling it reaches for pandas (read_excel, read_csv, to_excel).

The important detail: openpyxl writes formula strings but does not compute them. So when a deliverable depends on formula results, the skill recalculates the workbook headlessly (LibreOffice in --headless mode) so saved values match the formulas. It inspects existing files before editing so it doesn't clobber sheets it wasn't asked to touch.

Usage example

curl -fsSL --create-dirs -o ~/.claude/skills/xlsx-skill/SKILL.md https://claudeskil.com/skills/xlsx-skill/SKILL.md

# then, in Claude:
"Open ~/Downloads/q2_sales.xlsx, add a 'Margin %' column =
 (Revenue-Cost)/Revenue formatted as a percentage, add a bar chart
 of revenue by region on a new sheet, and freeze the header row."

Claude loads the skill, edits with openpyxl, recalculates, and writes the file back (or to a new path you specify).

Tips & gotchas

• Formulas need recalculation. A freshly written =SUM(...) shows the formula until the workbook is recalculated. If you read a value-only copy without recalc, you'll get None for formula cells.
• .xlsm macros are preserved when you keep the macro-enabled format, but openpyxl won't author or run VBA — it round-trips existing macros.
• CSVs carry no formatting or types. Datatypes are inferred on read; specify expected types when precision matters (e.g. ZIP codes that shouldn't become integers).
• Large workbooks: prefer pandas for data-heavy transforms and openpyxl for styling, rather than looping cells in Python.

FAQ

Does it keep my existing charts and styles? Yes — it edits in place through openpyxl, so untouched sheets, styles, and charts survive the round-trip.

Can it output a Word doc or Google Sheet instead? No. The deliverable is always a spreadsheet file. Use the docx skill for Word; Google Sheets needs the Sheets API, not this skill.

Will SUMIFS and VLOOKUP results be correct in the saved file? Yes, after the headless recalculation pass that the skill runs before saving.