xlsx

name	xlsx
description	Spreadsheet creation guidance for Doable's spreadsheet-builder MCP App. Adapted from the Anthropic xlsx skill — focuses on real data, hierarchical column structure, formulas (never hardcoded sums), and standards-compliant Office Open XML output via exceljs.

Spreadsheet design guide

Adapted for Doable's spreadsheet-builder MCP App. The actual file is rendered server-side with exceljs.

Hard requirements

Use formulas, never hardcoded calculations

• Totals: =SUM(B2:B10) — never compute the number yourself.
• Percent share: =B2/$B$11 — anchor the denominator with $.
• Growth: =(C2-B2)/B2.
• Lookups: =VLOOKUP(A2, Assumptions!A:B, 2, FALSE) — split data and assumptions into separate sheets when relevant.

Zero formula errors

• No #REF!, #DIV/0!, #VALUE!, #NAME?, #N/A.
• Verify: sums match a manual spot-check, ranges include all data rows, no division by an unset cell.

Real data, not placeholders

• Real names, real numbers, real categories.
• 8–40 rows is the sweet spot. Don't pad with "Item 5", "Item 6".

Color/format conventions

When the topic is a financial model, default to:

Role	Convention
Hardcoded inputs	Plain numbers (engine renders blue is optional)
Formulas	Plain numbers (engine renders black)
Currency	format: "currency" → renders $#,##0.00
Percent	format: "percent" → 0.18 in the cell renders as 18.0%
Years	format: "text" → keeps 2024 from being treated as a number
Dates	format: "date" → ISO string in cell, renders yyyy-mm-dd

The engine handles a styled header row (dark fill, white bold text) and zebra-striped data rows automatically — no need to specify per cell.

Choosing a kind

kind	When to use	Typical structure
data	Pure tabular dataset, no totals	Header + rows
budget	Financial plan / costs	Categories × periods + totals row + variance
tracker	TODO / project tracker	Item, owner, status, due, priority, notes
schedule	Calendar / agenda	Date, time, attendees, topic, duration
report	KPI dashboard + detail	Summary sheet + per-section sheets
comparison	Decision matrix	Options × criteria + score + total

Structure rules

• ONE topic per sheet. Use multiple sheets when the data is genuinely multi-faceted (Inputs, Calculations, Outputs).
• Sheet 1 = the most important / summary view.
• Add a separate Assumptions sheet for inputs that drive multiple formulas — let users tweak a single cell to flow through everything.
• Always set freezeHeader: true so the header row sticks while scrolling.
• Set sensible column widths: 10–14 for numbers, 18–28 for free text, 30+ for note/description fields.

What NOT to do

• ❌ Sum in JavaScript and put the number in the cell. Use =SUM(...).
• ❌ Use '2024 or other text tricks for years — set format: "text" on the column.
• ❌ Use percent string "18%" — put 0.18 in the cell with format: "percent".
• ❌ Mix numbers and strings in the same numeric column.
• ❌ Create one giant sheet when 2–3 cleanly separated sheets would read better.
• ❌ Use sheet names with [ ] : * ? / \ — the engine strips them but it indicates poor naming.