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
inchCALC+
PRO LEVEL [FOOT • INCH • FRACTION] CALCULATOR
$4.99 · In-app purchases
PRICE
$4.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 3.7
17 ratings · Top 50%
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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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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Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for inchCALC+: 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
Expand the list of units available for conversion.
Assumption to check: Limited unit options for conversion
Validate with people who use this workflow before building.
Hypothesis 2
Implement onboarding tutorials to guide users.
Assumption to check: UI can be cluttered for new users
Validate with people who use this workflow before building.
Hypothesis 3
Add a feature to save and view past conversions.
Assumption to check: Lack of advanced features like history tracking
Validate with people who use this workflow before building.
Hypothesis 4
Clarify subscription benefits and features upfront.
Assumption to check: In-app purchases can be confusing
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
PRO LEVEL [FOOT • INCH • FRACTION] CALCULATOR MACWORLD **** "inchCALC+'s ease of use coupled with its advanced features make this an uncommonly good addition to a crowded genre." 3/9/09 inchCALC+ is a State-of-the-Art Construction Calculator / Conversion Calculator for people who work with the FEET• INCH• FRACTION dimensions used on common rulers and tape measures. These dimensions are shear drudgery when you have to manually add or subtract them --- let alone multiply, divide or convert to other measurement units. If you are a builder, contractor, sub-contractor, architect, engineer, artist, designer, student, homemaker or DIYer, you know the importance of working with accurate dimensions. inchCALC+ transforms your iPhone / iPod Touch into a FT• IN• FRACTION construction calculator that inputs and outputs dimensions exactly as they appear on a tape measure. Dedicated and held construction calculators with similar functions are very expensive. With inchCALC+ you can inexpensively perform the functions of those calculators on your iPhone / iPod Touch. Easy conversions to other measurement units: -FT• IN • FRACTION -IN • FRACTION -decimal inches -decimal feet -millimeters -centimeters -meters -kilometers -acres -yards -miles Built-in TRIANGLE FUNCTION -- Enter any two & inchCALC+ automatically solves for the other two: -rise -run -diagonal -pitch Selective Keyboard Orientation for Left Handed or Right Handed users DUAL MODES: -inchCALC for quickly working with simple measurements -inchCALC+™ for working with more complex problem solving -Built-in Functions: √2, X2, π, %, +/- See further details & User Guide on our website below:
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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
Zustand
React Navigation
React Native Paper
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.
