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
Calculator HD Pro
A colorful calculator with big buttons, comprehensive features, and extensive customization
$9.99 · In-app purchases
PRICE
$9.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.8
11,192 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 included17 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
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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 Calculator HD Pro: map the core Utilities 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
Add more scientific features like graphing and advanced calculations.
Assumption to check: Limited advanced mathematical functions compared to competitors
Validate with people who use this workflow before building.
Hypothesis 2
Allow users to customize button styles and layouts.
Assumption to check: No ability to customize button layout or themes
Validate with people who use this workflow before building.
Hypothesis 3
Introduce features for complex number calculations and matrix support.
Assumption to check: Lack of support for complex numbers and matrices
Validate with people who use this workflow before building.
Hypothesis 4
Optimize app performance for older iOS devices.
Assumption to check: Inconsistent performance on older devices
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
A colorful calculator with big buttons, comprehensive features, and extensive customization. Used by millions. Completely ad-free. SEE EVERY STEP ・Dual-line display - shows your input and result simultaneously ・Multi-line input for long equations ・Tap & hold to move the cursor or copy and paste where you want SAVE YOUR WORK ・History saves every calculation with time and date ・Label important calculations for easy reference ・Email single calculations or complete history ・Swipe down to review previous work CUSTOMIZE EVERYTHING ・6 layouts including extra-large button options ・10 color themes plus Dark Mode ・Adjustable font size and bold text ・Left-handed mode ・Show or hide features you don't need SCIENTIFIC FUNCTIONS ・Full scientific calculator when needed ・Memory buttons with values displayed ・Percentage and backspace buttons ・Automatic scientific notation ・VoiceOver accessibility OPTIONAL IN APP PURCHASES ・Today View Widget (iOS 17 and below) ・Multiple History Tapes ADDITIONAL FEATURES ・Customizable button symbols and decimal settings ・Multiple backspace button styles ・iPad Split View and 3D Touch support ・Gesture controls for quick access URL Scheme: calculatorhdpro://
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-clipboard
expo-router
react-native-reanimated
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.
