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
Coffee Calculator: Brew Ratios
Stop ruining good coffee with bad math
$2.99 · In-app purchases
PRICE
$2.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 5.0
3 ratings · Top 5%
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 included16 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 Coffee Calculator: Brew Ratios: map the core Food & Drink 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 a guide or tips section to educate users on proper brewing techniques.
Assumption to check: Users often find it hard to get accurate brew ratios without extensive knowledge.
Validate with people who use this workflow before building.
Hypothesis 2
Allow users to save favorite ratios or brew settings.
Assumption to check: Limited customization options for user preferences.
Validate with people who use this workflow before building.
Hypothesis 3
Add a history feature to allow users to see past brews and ratios.
Assumption to check: No historical tracking of previous brews.
Validate with people who use this workflow before building.
Hypothesis 4
Clearly outline benefits of in-app purchases to enhance user experience.
Assumption to check: In-app purchases are not well explained.
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
Stop ruining good coffee with bad math. Coffee Calculator takes the guesswork out of brewing, so you can focus on what matters - enjoying perfect coffee. We've all been there. You switch from your V60 to AeroPress and suddenly your ratios are all wrong. You're brewing for friends and can't figure out how much coffee you need. Or you're down to your last few grams of beans, wondering how much water will salvage this situation. One wrong calculation and you're stuck with a disappointing cup of coffee. INSTANT CALCULATIONS, PERFECT RATIOS Type in how much coffee you have - instantly see the water needed. Or enter your water amount and get the exact coffee required. No more mental math before caffeine. No more wasted beans. Just perfect ratios every time. ALL YOUR METHODS, ONE APP • V60 & Chemex - nail your daily pour-over • AeroPress - perfect ratios you'll actually remember • French Press - scale up confidently for guests • Espresso - quickly dial in your dose-to-yield ratio • Cold Brew - get concentrate ratios right • Custom Methods - save your perfect ratios for different beans THE DETAILS THAT MATTER • Switch units instantly - grams, ml, ounces • Large buttons designed for wet hands • Remembers your favorite brew method • Syncs across all your devices • Clean, simple interface - no clutter, just coffee PERFECT FOR • Coffee lovers who switch between brew methods • Anyone who's ever Googled "coffee to water ratio" at 6am • People brewing different amounts throughout the day • Home baristas ready to experiment with ratios • Those expensive bean buyers who refuse to waste a gram Join coffee lovers who've stopped guessing and started brewing better. Download Coffee Calculator now - your morning coffee will thank you.
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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
React Navigation
React Native Paper
Async Storage
TypeScript
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.
