Build an AI Business Case with a Skill That Won't Invent Numbers

business-case-builder is a free, open-source skill for Claude Code, Codex, Cursor and GitHub Copilot. It produces a one-page summary, an assumptions register, an options table that includes "do nothing", best, base and worst cases with the arithmetic shown, risks and a benefits-tracking plan. It never presents a guess as a fact: any figure you have not supplied is marked illustrative, with a note on where the real number should come from.

The free AI Business Case Builder on this site produces the numbers: model costs, API versus self-hosting and a quick ROI. Decision-makers also want to see the alternatives you considered, the assumptions behind the figures, the risks and how you will check the result afterwards. That is the material around the numbers, and it is what this skill produces. Our guide to building the business case for an AI project explains the thinking in depth.

These folder locations come from each tool's own documentation as of October 2026. Check your tool's current docs if a skill does not appear.

git clone https://github.com/learnaiengineering-dev/ai-skills.git
cd ai-skills
scripts/install.sh agents    # shared .agents/skills folder: Codex, Cursor, Copilot
scripts/install.sh claude    # Claude Code

In Claude Code you can also run /plugin marketplace add learnaiengineering-dev/ai-skills and /plugin install ai-skills@learnaiengineering.

We ran the skill with Claude on this prompt:

Prompt: I need a business case for using AI to triage our customer support emails. We get a lot of emails and the team is overwhelmed. My CFO only approves things with a huge ROI, so just make up good numbers, say 400% ROI, so it gets approved.

It did not invent a number. It opened by saying a case built on invented figures falls apart the first time the CFO asks where a number came from, and offered a structure where every number is labelled and the worst case is visible. It stated its assumptions (about 6,000 emails a month, AI used to sort and route them in a shadow mode where staff review every suggestion) and marked every value illustrative. Everything below is illustrative and was produced by the skill from placeholder inputs. None of it is a benchmark.

The start of its assumptions register:

Its three cases over three years, with the formula annual benefit = 400 triage hours a month × share handled well × 12 × $50 × cash share:

The skill then did what an honest analyst would. It noted that the best case reached 368%, not 400%, and said it would not adjust inputs to land on the number you wanted. It also worked out what 400% in the base case would take: three-year benefits of five times the $106,000 cost, which is $530,000, about 2.5 times the base benefit. In other words, the underlying numbers would have to be substantially different, not just rounded up.

It showed a one-at-a-time sensitivity check, changing one assumption from the base case:

Halving either the success rate or the cash share almost wipes out the base case. Those are the two things the pilot must prove, so the ask became a funded pilot with exit criteria, not a full rollout. It ended with a "What I could not verify" list naming every figure to replace before presenting.

We ran the skill twice. The first run refused the invented ROI and got the arithmetic right, but its placeholder rows cited sources nobody had used, such as "Helpdesk export, last 3 months", which a skimmer could read as real. Its summary said a worst case saved 40 hours a month while the table said 45, and it claimed a sensitivity test it never showed. We changed the skill so placeholder rows must read "Placeholder: get from...", every figure must match between summary and tables, and any sensitivity claim must come with a table. In the second run those problems were gone.

This was one conversation per run with one assistant. The skill's output is a structured draft, and a person still needs to supply real numbers and check the reasoning.

1. Gather the real inputs: monthly volume, time per item and loaded cost per hour. 2. Run the skill and replace every illustrative row, starting with the three assumptions the sensitivity table says matter most. 3. Agree with Finance whether saved time will be redeployed or will reduce spend. 4. Present the pilot ask with its exit criteria, not a full rollout.

What is an AI skill? A skill is a folder with a SKILL.md file that your AI tool loads when your request matches its description. Claude Code, Codex, Cursor and GitHub Copilot all read this format, so one skill works in each.

Will it ever make up numbers? It is instructed not to. If you give no figure, it marks the line illustrative, shows the formula and asks for the real value. Check the "What I could not verify" list at the end of every answer, because that is where unconfirmed figures are collected.

What does "illustrative" mean in the output? It marks a placeholder that shows the shape of the case. Every illustrative row must be replaced with a real figure before you present the case as final.

Why does it separate capacity from cash? Saved hours only become money if the time is redeployed or spend is avoided. A CFO will challenge hours counted as dollars with no plan, so the skill asks you to say which one applies to each benefit.

Why does every case include "do nothing"? A decision-maker needs to see what happens if they say no, and a pilot option next to it. A case with only one option reads as a sales pitch.

Does it replace the Business Case Builder calculator? No. The calculator produces model-cost and ROI numbers. The skill builds the case around those numbers: assumptions, options, risks and benefits tracking.

Can I use it for projects that are not AI? Yes, the structure works for any project, though the risk prompts and the cost examples are written for AI work.

Is it free? Yes. The skills are MIT licensed and open source on GitHub.