Document XLSX Skill — Quick Reference

This skill enables creation, editing, and analysis of Excel spreadsheets programmatically. Claude should apply these patterns when users need to generate data reports, financial models, automate Excel workflows, or process spreadsheet data.

Modern Best Practices (Jan 2026):

• Treat spreadsheets as software: clear inputs/outputs, auditability, and versioning.
• Protect data integrity: control totals, validation, and traceability to sources.
• Accessibility: labels, contrast, structure; use Excel's Accessibility Checker; meet procurement/regulatory requirements when distributing externally.
• If distributing in the EU or regulated contexts, follow applicable accessibility requirements (often aligned with EN 301 549 / WCAG).
• Ship with a review loop and an owner (avoid "mystery models").
• Security: treat untrusted input/workbooks as hostile (formula injection, external links, hidden content, macros).

Quick Reference

Guardrails and Caveats

• Formula calculation: libraries write formulas; Excel computes results when opened. If you need computed values server-side, calculate in code and write values (or use a dedicated formula engine).
• Pivot tables: programmatic creation is limited. Prefer pandas summaries (pivot tables as data) or Excel automation (xlwings/Office Scripts/VBA) if you truly need native pivots.
• Macros: openpyxl can preserve existing VBA (keep_vba=True) but does not author macros; never generate or execute macros from untrusted input.
• Spreadsheet injection: never put untrusted strings into formula fields; write them as text values and validate/sanitize user-provided data used in exports.

Core Operations

Create Spreadsheet (Node.js - exceljs)

import ExcelJS from 'exceljs';

const workbook = new ExcelJS.Workbook();
const sheet = workbook.addWorksheet('Sales Report');

// Headers with styling
sheet.columns = [
  { header: 'Product', key: 'product', width: 20 },
  { header: 'Quantity', key: 'qty', width: 12 },
  { header: 'Price', key: 'price', width: 12 },
  { header: 'Total', key: 'total', width: 15 },
];

// Style header row
sheet.getRow(1).font = { bold: true };
sheet.getRow(1).fill = {
  type: 'pattern',
  pattern: 'solid',
  fgColor: { argb: 'FF4472C4' }
};

// Add data
const data = [
  { product: 'Widget A', qty: 100, price: 10 },
  { product: 'Widget B', qty: 50, price: 25 },
];

data.forEach((item, index) => {
  sheet.addRow({
    product: item.product,
    qty: item.qty,
    price: item.price,
    total: { formula: `B${index + 2}*C${index + 2}` }
  });
});

// Add totals row
const lastRow = sheet.rowCount + 1;
sheet.addRow({
  product: 'TOTAL',
  total: { formula: `SUM(D2:D${lastRow - 1})` }
});

// Currency formatting
sheet.getColumn('price').numFmt = '$#,##0.00';
sheet.getColumn('total').numFmt = '$#,##0.00';

await workbook.xlsx.writeFile('report.xlsx');

Create Spreadsheet (Python - openpyxl)

from openpyxl import Workbook
from openpyxl.styles import Font, PatternFill

wb = Workbook()
ws = wb.active
ws.title = 'Sales Report'

# Headers
headers = ['Product', 'Quantity', 'Price', 'Total']
for col, header in enumerate(headers, 1):
    cell = ws.cell(row=1, column=col, value=header)
    cell.font = Font(bold=True, color='FFFFFF')
    cell.fill = PatternFill(start_color='4472C4', end_color='4472C4', fill_type='solid')

# Data
data = [
    ('Widget A', 100, 10),
    ('Widget B', 50, 25),
    ('Widget C', 75, 15),
]

for row_idx, (product, qty, price) in enumerate(data, 2):
    ws.cell(row=row_idx, column=1, value=product)
    ws.cell(row=row_idx, column=2, value=qty)
    ws.cell(row=row_idx, column=3, value=price)
    ws.cell(row=row_idx, column=4, value=f'=B{row_idx}*C{row_idx}')

# Totals row
total_row = len(data) + 2
ws.cell(row=total_row, column=1, value='TOTAL')
ws.cell(row=total_row, column=4, value=f'=SUM(D2:D{total_row-1})')

# Number formatting
for row in range(