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
Karat Kalculator
*Price updates have been fixed
$1.99 · In-app purchases
PRICE
$1.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 2.7
7 ratings · Below Average
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 included15 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 Karat Kalculator: 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 advanced features like gold price tracking, graphing historical values.
Assumption to check: Limited features compared to competitors
Validate with people who use this workflow before building.
Hypothesis 2
Focus on a modern, clean design with user testing.
Assumption to check: Poor user reviews regarding UI
Validate with people who use this workflow before building.
Hypothesis 3
Implement a feature to save and revisit previous calculations.
Assumption to check: No ability to save calculations
Validate with people who use this workflow before building.
Hypothesis 4
Include tutorials on gold karat and value calculations.
Assumption to check: Lack of educational content
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
*Price updates have been fixed. Thank you for your patience.** Mid-States Recycling & Refining’s famous Karat Kalculator is now available on your iPhone! Try our web version at www.karatkalculator.com. The Karat Kalculator is a tool to estimate the practical value of your Karat Gold Scrap. Simply select your measurement unit on the main Kalculator page and enter your weights under each specific karat field. To calculate the total value of your scrap gold, you can tap calculate or the results tab on the bottom of the screen. The results screen will show you the total estimated net value of your refining lot minus any associated charges, plus much more useful information. When you first open the Karat Kalculator app it will obtain the most current gold price from www.midstatesrecycling.com. This price will be displayed on the Kalculator page and the Gold Price page. The gold price can be adjusted to any future price of your choice by either tapping the gold price on the Kalculator page or changing it on the Gold Price page. In our 40 years of experience we have found most karat gold jewelry scrap to average approximately a ½ karat under its plumb stamp. Because of this we have built the Karat Kalculator to mimic the recoveries for each grade of Karat Gold that our historical data indicates. Final settlements will be based on the actual melt & assay results at appropriate current gold market, less applicable treatment and refining charges. Mid-States Recycling works with trade only. A valid business license in the Jewelry, Pawn, 2nd Hand Buy/Sell, or Scrap Metal Dealer is required.
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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
Axios
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.
