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
Caff: Caffeine & Sleep Tracker
Know exactly how much caffeine is in your system
$0.99 · In-app purchases
PRICE
$0.99
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's included17 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 Caff: Caffeine & Sleep Tracker: map the core Health & Fitness 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
Implement a more detailed logging system with customizable caffeine types.
Assumption to check: Users often find it hard to track caffeine intake accurately.
Validate with people who use this workflow before building.
Hypothesis 2
Provide a guided questionnaire to help users rate their sleep quality.
Assumption to check: Sleep quality scoring can be subjective.
Validate with people who use this workflow before building.
Hypothesis 3
Add data visualization to analyze caffeine intake trends.
Assumption to check: Limited insights on caffeine consumption patterns.
Validate with people who use this workflow before building.
Hypothesis 4
Enhance the paywall with clear benefits of premium features.
Assumption to check: In-app purchase options may be unclear.
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
Know exactly how much caffeine is in your system. Right now, and at bedtime. Caff tracks your caffeine intake and models how it decays in your body using a scientifically-based half-life formula. Log a coffee in seconds, then watch the burndown chart show you your caffeine curve for the next 12 hours. SLEEP SMARTER Set your bedtime once. Caff calculates how much caffeine will still be in your system when you try to sleep, estimates how many minutes of sleep you'll lose, and shows you a "Last Call" time, the latest you can safely drink caffeine tonight. TRACK YOUR INTAKE • Preset drinks: coffee, espresso, tea, energy drinks and more • Create custom drinks with a name, emoji, and mg amount • Personal daily caffeine limit with a live progress bar • Full history grouped by day, swipe to delete 5 HOME SCREEN WIDGETS Summary · Burndown chart · Sleep forecast · Today's log · Weekly chart, all updating live from a shared data container. APPLE HEALTH Every entry is written to Apple Health as dietary caffeine. Delete an entry in Caff and the Health sample is removed too. No reads, your Health data stays private. 100% PRIVATE No account. No cloud. No data collection. Everything lives on your device.
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
Zustand
react-native-chart-kit
react-native-datepicker
@react-navigation/native
BUILD KIT DIFFICULTY
Intermediate
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.
