---
name: spreadsheet-model-builder
description: "Lays out a spreadsheet model with separated inputs, stated assumptions, traceable formulas, and a summary sheet, so a reviewer can follow every number. Use when a spreadsheet model is needed to answer a planning or finance question, with separated inputs, assumptions, formulas, and a summary a reviewer can audit. Do not use for cleaning or analysing an existing dataset or writing macros. Related topics: data, business."
---

# Spreadsheet Model Builder

Lays out a spreadsheet model with separated inputs, stated assumptions, traceable formulas, and a summary sheet, so a reviewer can follow every number.

## When to use

Use this skill when a spreadsheet model is needed to answer a planning or finance question, with separated inputs, assumptions, formulas, and a summary a reviewer can audit. Do not use it for cleaning or analysing an existing dataset or writing macros.

## Workflow

1. Ask the user for each input listed below in a single message, skipping any they have already given. Where options are listed, offer them, but accept other answers too.
2. Restate the question the model answers and choose the time horizon and scenario structure that serve it.
3. Lay out separate sheets for Inputs, Assumptions, Calculations, and Summary, with each input given a unit and source.
4. Write the row-by-row formulas for the chosen tool, referencing input cells and keeping each row's formula consistent.
5. Add a scenario switch and reconciliation checks that show OK or ERROR.
6. Describe the Summary sheet and give the reviewer a short audit path.

## Inputs

- **The question the model answers** (longer free text)
- **Time horizon** (choose one: Monthly for 1 year, Monthly for 3 years, Quarterly for 5 years, Annual for 10 years)
- **Key inputs** (longer free text)
- **Assumptions to test** (longer free text)
- **Scenarios** (choose one: One case, Base and downside, Base and upside and downside)
- **Tool** (choose one: Excel, Google Sheets)

## Output

A sheet-by-sheet layout, row-level formulas for the chosen tool, the check cells, the Summary design, and a short audit note.

## Prompt template

Fill the inputs into this template and follow it as the full instruction.

### Spreadsheet Model Builder

Design a spreadsheet model for the question below.

- The question the model answers: {{The question the model answers}}
- Time horizon: {{Time horizon}}
- Key inputs: {{Key inputs}}
- Assumptions to test: {{Assumptions to test}}
- Scenarios: {{Scenarios}}
- Tool: {{Tool}}

Plan the workbook as separate sheets: Inputs (every hard-coded number in one place, with units and a source), Assumptions (clearly marked guesses with a low, base, and high value), Calculations (formulas only, one row per line item, time across columns), and Summary (the answer, a small table, and one chart). Never hard-code a number inside a formula; reference the input cell. Keep formulas consistent across a row so they can be filled right. Use named ranges for the important inputs and a scenario switch cell that picks which assumptions flow through. Add checks: totals that must reconcile, with a visible OK or ERROR cell.

Return the sheet layout, row-by-row structure with the actual formulas in the chosen tool, the check cells, and a short note on how a reviewer should audit it.

## Pitfalls

- Typing a growth rate inside a formula, so nobody can find or change it later.
- Mixing inputs, calculations, and results on one sheet, which makes errors invisible to a reviewer.
- Treating a guess as a fact by leaving assumptions unmarked and unsourced.