Claude Excel skill (xlsx)

Claude can return a real Excel file with formulas that recalculate when you change an input. The work is done by Anthropic's Excel skill, ID xlsx, one of four pre-built document skills. This page covers what it does, the rules it follows, how to use it and what to check. New to skills? Start with how Claude Skills work.

What the skill does

The skill triggers whenever a spreadsheet is the main input or output: opening, editing or fixing .xlsx, .xlsm, .csv and .tsv files, adding columns, writing formulas, formatting, charting, cleaning messy data, building a workbook from scratch, or converting between table formats. Its SKILL.md sets rules for every file it produces:

• Formulas, never pasted results. A total is written as =SUM(B2:B9), so the sheet updates when inputs change.
• Zero formula errors. Claude recalculates the workbook with a script and does not ship while errors remain.
• Your spec, literally. Exact tab names, column headers and formulas you asked for.
• Your file's conventions win. When editing, Claude writes only to the input cells and leaves existing formulas alone.
• Assumptions on the page. Hardcoded numbers get a note or source next to them.

For financial models it follows a common color code: blue text for inputs, black for formulas, green for links to other sheets.

When to use it

• Turning a pasted table or CSV export into a clean, formatted workbook.
• A budget, forecast or pricing model you will keep updating.
• Pulling tables out of a PDF into a sheet, together with the PDF skill.

For analysis across a database or many files, the data plugin adds SQL and validation steps. Our data prompts and finance prompts help frame the question first.

How to install it

Claude.ai: built in. Turn on "Code execution and file creation" under Settings > Capabilities. The help center lists it on Free, Pro, Max, Team and Enterprise plans.

Claude API: add xlsx to the container parameter with the code execution tool.

Claude Code: not bundled. Install Anthropic's published copies:

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

Example request

Build an Excel model of [business or project] for the next [number] months. Put every assumption ([list: price, volume, costs]) on an "Inputs" sheet in blue, and calculate everything else with formulas. Add a summary chart. Note the source of each assumption next to it.

Limits

• The skill avoids XLOOKUP, FILTER, SORT, UNIQUE and SEQUENCE, because its sandbox cannot evaluate them reliably. Expect INDEX and MATCH instead.
• A clean recalculation proves formulas run, not that they are right. The SKILL.md itself warns that a wrong range gives wrong numbers with no error, so spot-check key totals.
• Links to other workbooks can be lost when the file is re-saved, and .xlsm macros survive only when Claude opens the file with macros kept.
• It works on Excel files. It does not edit Google Sheets through their API.
• The repository copy is source-available, not open source.

FAQ

Can Claude create an Excel file with formulas?

Yes. The skill's first rule is to write formulas instead of pasted values, and it recalculates the file to check for errors.

Is there an Excel skill for Claude Code?

Not bundled. The document-skills plugin from Anthropic's skills repository adds it.