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
My Calculator (incl. currency)
//*** version 6 for ios 17 and watchos 10 ***//
$0.99 · In-app purchases
PRICE
$0.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.9
8 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
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A product spec, screen plans, and build steps for your coding agent.
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What should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
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/
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 My Calculator (incl. currency): map the core Finance 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
Include more currencies and real-time exchange rates.
Assumption to check: Limited currency options compared to competitors.
Validate with people who use this workflow before building.
Hypothesis 2
Add a feature to save and view past calculations.
Assumption to check: Lack of advanced features like history tracking.
Validate with people who use this workflow before building.
Hypothesis 3
Offer a more flexible pricing model or free trial.
Assumption to check: Subscription model may deter users.
Validate with people who use this workflow before building.
Hypothesis 4
Simplify UI for better user experience.
Assumption to check: User interface can be overwhelming.
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
//*** version 6 for ios 17 and watchos 10 ***// //*** including currency exchange calculator for iphone, ipad and apple watch***// the only one pocket calculator for iphone, ipad, apple watch, apple tv and also works as today widget, message extension and keyboard. simple pocket calculator supports parentheses and memory functions. see what you calculate. also as today widget, message extension or keyboard possible - just enable it. calculate a number of days to an given date or show the weekday name of a given date. currency exchange calculator available for iphones and apple watch. please note: the apple watch calculator is small. anyhow all on a single screen and the calculation step is always visible. apple watch: you can choose between three screens: - big buttons // operators left - big buttons // operators right - smaller buttons // with parentheses in addition you can disable the function screen. then it is a simply calculator. just go to the watch settings. support for deep pressure gestures - or long press on older iphones/ ipads: m+ -> m- mr -> show only memory c -> ac f(x) -> display currency converter pi -> random number between 0...1 e -> random integer number between 0...n % -> deferred payment credit/ monthly rate (i = interest rate, m = month) ( -> add open parenthesis at beginning ) -> add open and close parentheses (⋯) -> add close parenthesis define own currency in settings app (ios settings/ watch settings) select own currency as from currency, select a different currency as to currency, type in exchange rate, long press own currency. now all exchange rates for the other currencies will be calculated and stored. on watch just deep press on currency calculator. any questions or wishes -> support // email
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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
axios
react-native-gesture-handler
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.
