XLSX

XLSX is the official Anthropic Agent Skill that lets Claude open, read, edit, and create spreadsheet files — .xlsx, .xlsm, .csv, and .tsv — and deliver a finished spreadsheet as the output. Use it any time the primary input or output is a spreadsheet: adding columns and formulas, applying number formats, building charts, cleaning messy tabular data, or converting between tabular formats.

What is XLSX?

XLSX is a skill in Anthropic's official anthropics/skills repository that teaches Claude a repeatable workflow for working with Excel and CSV files. It pairs pandas for data analysis and bulk operations with openpyxl for formulas, cell formatting, and Excel-specific features, and ships a scripts/recalc.py helper that drives LibreOffice to recalculate every formula and scan for errors. The deliverable is always a real spreadsheet file, not a script or a Word report.

What it does

• Opens and reads existing .xlsx, .xlsm, .csv, and .tsv files to analyze or summarize their contents
• Edits spreadsheets in place — adding columns, inserting rows, writing live Excel formulas (=SUM, =AVERAGE, growth rates), and applying fonts, fills, and number formats
• Creates new spreadsheets from scratch or from other data sources
• Builds charts and applies professional formatting, including industry-standard financial-model color coding (blue inputs, black formulas, green intra-workbook links, red external links)
• Cleans and restructures messy tabular data — malformed rows, misplaced headers, junk data — into a proper spreadsheet
• Converts between tabular file formats

How it works

Install the skill, then ask Claude to do something with a spreadsheet. Claude chooses the right tool — pandas for data analysis and export, openpyxl for formulas and formatting — loads or creates the workbook, writes real Excel formulas instead of hardcoding computed values, then runs python scripts/recalc.py output.xlsx so LibreOffice recalculates the file and returns JSON listing any errors (#REF!, #DIV/0!, #VALUE!, #NAME?). Claude fixes flagged cells and recalculates until the model is clean. Every model is delivered with zero formula errors.

Who it's for

Analysts, finance teams, operations and RevOps staff, founders, and anyone who lives in spreadsheets and uses Claude (Claude.ai, Claude Code, or the Claude API) to produce or repair Excel and CSV files. It is especially useful for financial modeling, where it enforces assumption cells, cell references over hardcoded values, and standard number formats (currency as $#,##0, percentages at one decimal, multiples as 0.0x, negatives in parentheses).

What you can build

• Financial models and three-statement projections with assumption-driven formulas
• Budget, forecast, and KPI trackers that recalculate when inputs change
• Cleaned and normalized datasets exported from raw CSV or TSV dumps
• Formatted reporting workbooks with charts and consistent professional fonts
• Format conversions between .csv, .tsv, and .xlsx

Why it matters

Spreadsheets break when calculated values are hardcoded or when formula errors slip through. This skill makes Claude treat the spreadsheet as a living model: it uses formulas so the file stays dynamic, preserves existing template conventions when editing, and verifies the result with a real recalculation pass. That is the difference between a one-off export and a workbook a team can keep using.

1. Install with the skills CLI

npx skills add anthropics/skills --skill xlsx

2. Or add it as a Claude Code plugin

/plugin marketplace add anthropics/skills
/plugin install document-skills@anthropic-agent-skills

3. Use it

Point Claude at a spreadsheet and say what you want, for example: "Clean up the xlsx in my downloads and add a monthly revenue chart."