One task. One useful app.

The method

1. Keep the first job small

   In what situation would a colleague open the tool? Which one decision or action must they be able to complete? Other features can wait.

2. Define data and rules

   Give every field a type, unit and validation rule. Include formulas, rounding and invalid-input behaviour in the brief. A known formula does not need AI.

3. Design useful feedback

   Show what is missing, what was calculated and whether data survives closing the app. Start with sample data; connecting live business data is a separate implementation step.

A simple contribution check

Illustrative example. A sales coordinator checks contribution using a product's net selling price and direct cost. The example price is HUF 50,000 and the cost is HUF 35,000.

Contribution: 50,000 − 35,000 = HUF 15,000. Contribution as a percentage of sales: 15,000 / 50,000 × 100 = 30%. The app shows the amount and percentage separately. With a zero or missing selling price, it does not divide; it displays a helpful validation message. Markup on cost is a different measure and must have a different label.

Your worksheet

User and first task

Who opens the app, in what situation, and what must they be able to finish without help?

Fields and formulas

Name, type, unit, requirement, formula and rounding. Which inputs must prevent calculation?

Interface and data

What does the user enter, what result appears, and what remains after the app is closed?

Acceptance trial

Write normal, empty, zero and invalid cases with manually checked expected results.

Review checks

• A new user can complete the first task without help.
• Formulas and units can be checked manually.
• Invalid inputs do not produce misleading results.

Test with someone who did not build it

Give a colleague a sample case and watch where they get stuck. Fix that point before adding another feature.