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
MarginMate — Margin Calculator
The fastest margin calculator, on iPhone and Apple Watch.
$0.99
PRICE
$0.99
No in-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
N/A
No ratings yet
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 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 MarginMate — Margin Calculator: 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
Add options for advanced calculations like percentage changes and detailed reports.
Assumption to check: Limited functionality for complex margin calculations
Validate with people who use this workflow before building.
Hypothesis 2
Implement a history feature to save and view past calculations.
Assumption to check: No history tracking for previous calculations
Validate with people who use this workflow before building.
Hypothesis 3
Enhance UI with modern design patterns and user-friendly interactions.
Assumption to check: Basic user interface with minimal design elements
Validate with people who use this workflow before building.
Hypothesis 4
Introduce notifications for users to remind them to calculate margins regularly.
Assumption to check: No notifications or reminders for regular users
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
The fastest margin calculator, on iPhone and Apple Watch. Stop switching between apps. MarginMate is with you in one tap — on your wrist or in your pocket — so you can quote prices, check margins, and close deals without missing a beat. Smart calculation — enter any 2 values: · Cost + Margin % → Revenue & Profit calculated · Revenue + Cost → Margin & Profit calculated · Profit + Margin % → Revenue & Cost calculated Any combination works. MarginMate figures out the rest. Built for people who work with numbers: · Retailers pricing products on the shop floor · Sales reps quoting on the spot · Freelancers calculating their rates · Buyers checking supplier margins · E-commerce sellers managing markups Margin or Markup — your choice Switch between Margin % and Markup % mode in one tap. MarginMate adapts to how you think about pricing. History — every calculation saved Every result is automatically saved with date and time. Restore any previous calculation in one tap. Apple Watch — Digital Crown precision Scroll the Digital Crown to fine-tune values one unit at a time. Natural, fast, no friction. iPhone — Full keyboard input Tap any field to enter a value. Long-press any computed result to copy it to the clipboard. Configurable precision Choose 0 to 4 decimal places. Settings sync between iPhone and Watch. Simple. Fast. Focused. Four fields. One goal: your margin, instantly. I’m One-time purchase. No subscription. No ads. Pay once. Use forever.
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
Supabase
React Navigation
Zustand
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.
