Costing assistant — build, stress-test and explain a garment costing

What you get

A skill that turns a bill of materials plus your factory CM quote, packaging, testing, freight, duty and overhead figures into a costing sheet in a fixed 9-column CSV, computes subtotals and landed cost with the arithmetic shown next to each line, runs sensitivities (fabric price, wastage, FX), compares two factory quotes, measures the gap to a target cost and writes the costing memo. It never estimates a missing price, rate or duty — the line says TBC, every total says what it excludes, and the question goes on a list. Runs in Claude, ChatGPT, Gemini and Claude Code.

Use it for

• Build a costing sheet from a BOM and a CM quote, arithmetic shown on every line
• See what moves the landed cost: fabric price ±10 %, wastage +5 points, exchange rate ±5 %
• Compare two factory quotes normalised to one currency, quantity and incoterm
• Measure the gap to a target cost and list the levers with the change each needs
• Write the half-page costing memo for the handover meeting

What's inside

• SKILL.md — the skill: procedure, 9-column output format, arithmetic rules, self-checks, when to ask
• PROMPTS.md — Build · Update · Sensitivity · Compare two quotes · Target-cost gap · Costing memo
• templates/costing-sheet.csv — empty sheet with the standard lines by section and a summary block
• examples/costing-example.csv — the sheet filled once for a fictional field jacket, TBC where unknown
• examples/costing-memo-example.md — the costing memo written from that sheet, with sensitivities
• platforms/chatgpt-instructions.md — Custom GPT / Project instructions
• platforms/gemini-gem.md — Gem instructions
• platforms/claude-code/.claude/skills/costing-assistant/SKILL.md — Claude Code drop-in

Quick start

1. Unzip and open README.md.
2. Claude: Settings → Capabilities → Skills → upload SKILL.md. ChatGPT: paste platforms/chatgpt-instructions.md into a Project. Gemini: paste platforms/gemini-gem.md into a Gem. Claude Code: copy platforms/claude-code/.claude/ into your project.
3. Paste the Build prompt from PROMPTS.md with your BOM and the quotes you hold.

Preview — one prompt from the kit

Run sensitivities on this costing sheet for {{style}}: {{costing}}

Scenarios: (a) shell fabric unit cost +10 % and −10 %; (b) wastage +5 percentage points on all fabric lines; (c) exchange rate ±5 % on every line quoted in a foreign currency (rate used: {{fx_rate}}); (d) any scenario I add here: {{quotes}}

For each scenario recompute only the lines affected, propagate to duty if duty is a percentage of a base that changed, and give: lines changed · delta per unit · new landed cost. Put the results in one table, then two sentences on which lever matters most. Do not change the sheet.