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
NumPad: Calculator Keyboard
Type a number, get an answer.
$2.99 · In-app purchases
PRICE
$2.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.2
232 ratings · Top 30%
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 NumPad: Calculator Keyboard: 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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App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
Screenshots
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App Store description
Type a number, get an answer. NumPad puts a full numeric keypad and calculator right inside your iPhone keyboard. Type "1200*0.0825" and the answer floats above your cursor before you even reach for "=". Tap it to insert, or keep typing to refine. LIVE MATH, WHILE YOU TYPE Start any expression — "84.50*1.18", "250-20%", "3*12+40" — and a floating result chip appears above the cursor as you type. Same engine as the "=" key and Siri, with zero extra taps. KEYBOARDS FOR YOUR ACTUAL WORK Swap in a specialty key layout for what you're doing — six packs included: • Finance — currency symbols for fast price entry • Symbols & Science — π, √, ^, ° and math notation • Programmer — hex prefixes and bitwise operators • Date & Time — today's date or the current time in one tap • Units & Conversion — length, mass, temperature with a live offline converter • Cooking & Baking — fraction keys (½ ⅓ ¼) plus cups-to-millilitres converter PRO SHORTCUTS Long-press "%" for a two-step tax + tip calculator. Long-press "." for reusable text snippets. Long-press "0" for clipboard history. Long-press "=" for the unit and recipe converter. Every calculation lands on a running result tape you can revisit anytime. BUILT FOR THE LATEST iOS NumPad speaks Siri: "Calculate with NumPad," "Convert units with NumPad," and "Calculate a tip with NumPad" work the moment the app is installed — no setup. Every pack runs fully offline. On the latest iOS, the optional Glass theme uses real Liquid Glass, matched for light and dark mode. YOUR LAYOUT, YOUR CALL A custom keyboard with the layout you choose — full keypads, compact rows, your arrangement. If you enter numbers anywhere — payments, spreadsheets, expenses, code, recipes — NumPad pays for itself the first day.
Written user reviews are not shown here. Check current App Store reviews >
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
Provide users with more layout options and customization tools.
Assumption to check: Limited customization options for keyboard layouts.
Validate with people who use this workflow before building.
Hypothesis 2
Ensure consistent and responsive haptic feedback across all buttons.
Assumption to check: Inconsistent haptic feedback on button press.
Validate with people who use this workflow before building.
Hypothesis 3
Implement a feedback feature for users to report issues or suggest features.
Assumption to check: No option to feedback to developers directly from the app.
Validate with people who use this workflow before building.
Hypothesis 4
Add multi-language input support to cater to a wider audience.
Assumption to check: Lack of support for multi-language input.
Validate with people who use this workflow before building.
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
React Navigation
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BUILD KIT DIFFICULTY
Intermediate
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.
