Feature spec
Goal: Send a clear invoice after finishing a job.
- Add a client, line items, a due date, and payment instructions.
- Preview the total before exporting a PDF.
- Keep an editable draft if export fails.
App Overview
Fraction Calculator PRO #1
Fraction Calculator Plus - the best and easiest solution for fractions in everyday life
$3.99 · In-app purchases
PRICE
$3.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.9
752 ratings · Top 5%
Evidence scope: No current overall US chart position is available. Category-chart positions shown in discovery are a separate scope. Revenue is a directional model estimate, not verified earnings.
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Build Kit
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A product spec, screen plans, and build steps for your coding agent.
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What's included15 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
Preview a sample Build Kit No email needed
Illustrative example: an invoice app for independent contractors. Your kit is tailored to the app you choose; this is not its generated content.
Screen plan
Invoice editor: Client at the top, editable line items in the middle, total and preview action at the bottom.
States: Empty draft, validation errors beside each field, exporting, and a retry action that preserves the draft.
Differentiate and validate
Hypothesis: Contractors need faster repeat invoices more than more templates.
First experiment: Test duplicating a previous job with five contractors. Watch where they hesitate before expanding the feature set.
The full kit adds a phased build plan, evidence notes, tool prompts, and implementation guidance. It is a plan for your coding agent, not a finished app.
Usage: Mechanics are fair game; never reuse the original name, branding, assets, or verbatim copy.
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Free quick prompt For a smaller starting point
Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for Fraction Calculator PRO #1: map the core Productivity workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
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Opportunities
AI-GENERATED OPPORTUNITY HYPOTHESES
These are generated suggestions, not verified review quotations. Check current App Store reviews and speak with users before treating a possible gap as a requirement.
Hypothesis 1
Implement input validation and error messages to guide users.
Assumption to check: Users find it hard to input fractions accurately
Validate with people who use this workflow before building.
Hypothesis 2
Allow users to edit or delete specific history entries.
Assumption to check: Limited history management options
Validate with people who use this workflow before building.
Hypothesis 3
Add functionality for inputting and calculating mixed numbers.
Assumption to check: No support for mixed numbers
Validate with people who use this workflow before building.
Hypothesis 4
Include a step-by-step breakdown of calculations for better understanding.
Assumption to check: Lack of visual representation of calculations
Validate with people who use this workflow before building.
App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
App Store description
Fraction Calculator Plus - the best and easiest solution for fractions in everyday life. Calculate fractions: add, subtract, divide and multiply. Convert fractions to decimals easily. - Would you like time to check your children's maths exercises? Now that's no longer a problem because you can review fractions in seconds. - Do you need to adjust recipe quantities for a longer guest list? It will calculate the amounts in cups and teaspoons for you. - Are you working on a craft or construction project with dimensions in inches? Forget about double or triple calculations on paper. Use fraction for correct calculations. It's an easy-to-use fraction calculator with a large display and big buttons. Features: - The digits and buttons are clear and big, so they can be read at a glance from a distance. - Convenient triple keyboard display enables quick typing. You only need to type three times to enter “three and three quarters”! - Each fraction is automatically scaled down to its simplest form to make it easier for you. - NEW! Each result is also displayed as a decimal number. That makes the conversion a breeze. - Adding, subtracting, multiplying and dividing fractions has never been easier. With Fraction Calculator Plus, your mobile phone or tablet is by your side in everyday life.
Written user reviews are not shown here. Check current App Store reviews >
Screenshots
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Build scope
Plan a focused first version with your coding agent. These are planning assumptions, not a delivery guarantee.
Define the first version
Choose one audience and one core workflow. Use the kit to agree on its screens, data, and acceptance criteria before building.
Set boundaries
Decide which secondary features, integrations, and platform support can wait. Your version does not need to reproduce everything in the original.
Check the hard parts
Validate external services, specialist technology, data access, and ongoing costs for your chosen scope.
SUGGESTED BUILD STACK
React Native
Expo
Zustand
react-native-paper
react-hook-form
BUILD KIT DIFFICULTY
Starter
From the Build Kit assessment.
A reliable timeline needs an agreed scope and a technical check. Ask your agent to estimate the phases in BUILD_PLAN.md after that review.
