Spreadsheet Model Builder skill for Claude and Codex

Spreadsheet Model Builder as an AI skill. It asks for The question the model answers, Time horizon, Key inputs and 3 more, then does the rest. Free to install…

Install it once and Claude or Codex runs it for you. When your request matches, your AI loads the skill, asks for anything it is missing, and works through the template itself. Prefer to fill it in by hand? See the full prompt template.

Download the skill (.zip) · View SKILL.md

When it is used

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.

What it will ask you for

• 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)

How it works

1. Restate the question the model answers and choose the time horizon and scenario structure that serve it.
2. Lay out separate sheets for Inputs, Assumptions, Calculations, and Summary, with each input given a unit and source.
3. Write the row-by-row formulas for the chosen tool, referencing input cells and keeping each row's formula consistent.
4. Add a scenario switch and reconciliation checks that show OK or ERROR.
5. Describe the Summary sheet and give the reviewer a short audit path.

What you get

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

What it watches out for

• 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.

How to install

Claude.ai and the Claude desktop app

1. Download the skill .zip.
2. Open Settings, then Capabilities, and find Skills.
3. Choose Upload skill and select the .zip.
4. Ask Claude for help with the task. It loads the skill when your request matches.

Claude Code

1. Download the skill .zip.
2. Unzip it into ~/.claude/skills/ (or .claude/skills/ inside a project).
3. Start a new session. Claude Code loads the skill when your request matches.

Codex

1. Download the skill .zip.
2. Unzip it into ~/.agents/skills/ (or .agents/skills/ inside a project).
3. Codex picks it up on its own. Type $ and the skill name to use it, or just ask for the task.

Cursor

1. Download the Cursor rule (.mdc).
2. Save it in .cursor/rules/ inside your project.
3. Cursor's agent applies the rule when your request matches its description.

AGENTS.md (Codex, Cursor, and other coding agents)

1. Copy the AGENTS.md section.
2. Paste it into AGENTS.md at the root of your repository, creating the file if needed.
3. Coding agents that read AGENTS.md follow it when your request fits.