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!
Calculator! is an easy to use, beautifully packaged calculator for your iPad or iPhone that includes both a standard and scientific calculator.
$0.99 · In-app purchases
PRICE
$0.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.8
4,262 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.
Build your own version
Build Kit
Make this idea yours
A product spec, screen plans, and build steps for your coding agent.
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Combine features and design from your favorite apps.
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Make it yours Optional
What should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
What's included16 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 Calculator!: map the core Utilities workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
Preview ready. Verify your email to reveal and copy the full prompt.
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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 features like graphing, history tracking, and more advanced math functions.
Assumption to check: Limited functionality compared to advanced calculators
Validate with people who use this workflow before building.
Hypothesis 2
Enhance UI with themes and customizations.
Assumption to check: User interface is overly simplistic
Validate with people who use this workflow before building.
Hypothesis 3
Implement dark mode for better usability.
Assumption to check: Lack of dark mode support
Validate with people who use this workflow before building.
Hypothesis 4
Enable cloud sync for user history across devices.
Assumption to check: No cloud sync for history
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
Calculator! is an easy to use, beautifully packaged calculator for your iPad or iPhone that includes both a standard and scientific calculator. Our versatile calculator app allows you to: • Customize the look of the application by changing the leather color and background texture (iPad Only) • Choose between a basic calculator or scientific calculator with more than 30 scientific operations • Use both calculators in portrait or landscape mode • Take notes or draw with your finger on the Notes Tab • View and edit a history of your calculations on the History Tab • Use Airprint to print your notes or your calculation history • Email your calculation history or notes from within the app • View an equation of your current calculations • Calculate with accuracy to more than 75 significant digits • Use parenthesis and nested parenthesis in your calculations We wrote Calculator! to be the perfect calculator for budding math students and professionals alike.
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
Redux
React Navigation
TypeScript
React Native Async Storage
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.
