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
Loan Calculator +
*** Featured by Apple as 'What's Hot' ***
$1.99 · In-app purchases
PRICE
$1.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.7
152 ratings · Top 15%
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 Loan 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
Provide side-by-side comparison for multiple loans
Assumption to check: Limited loan scenario comparisons
Validate with people who use this workflow before building.
Hypothesis 2
Allow users to save and customize loan parameters
Assumption to check: Lack of user customization options
Validate with people who use this workflow before building.
Hypothesis 3
Implement offline functionality for calculations
Assumption to check: No offline access
Validate with people who use this workflow before building.
Hypothesis 4
Add graphs or charts for loan payment trends
Assumption to check: Limited visual representation of results
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
*** Featured by Apple as 'What's Hot' *** Loan Calculator has one aim - To SAVE YOU MONEY on your loan! If you're taking out a loan, looking to organise your loans, or want to pay off your loan early, then this is the perfect app for you. Try out various 'What-If' scenarios and quickly see how extra payments can save you a whole lot of time and money. You can enter any number of Monthly, Yearly or One Off extra payments, at any period during the loan. Then watch the total length and cost go down. You may be surprised by just how much! Easily visualise your cost savings in the simple and interactive charts. Just slide your finger along to see the costs for each year. 5-Stars - "...beautiful, simple graphs which make tricky decisions a whole lot easier." 5-Stars - "...really helped me to compare the different loan deals" *** Features *** -------------------- Visualise loan costs in simple, interactive charts: √ Organise any number of loans √ Support for mortgages, car loans, credit cards and many more √ See money saving effect of regular or one off Extra Payments √ Variable Rates support √ Calculate the 'True Cost', by including Tax, Insurance etc √ Email a PDF or HTML of the loan details √ Takes into account PMI for mortgages √ Monthly breakdown of costs (Amortization) √ Full support for fixed 'Initial Rates' e.g. interest free for 6 months √ Try out various 'What-If' scenarios √ Charts allow easy visualisation of the costs √ Make an informed choice by comparing loans √ Extra payments can 'Reduce Term' or 'Reduce Payments' √ Support for 'Repayment' or 'Interest Only' √ Set of quick calculators for instant answers √ Backup & Restore via Dropbox √ Passcode protection √ Elegant, simple and powerful user interface
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
React Navigation
React Native Paper
Zustand
Axios
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.
