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
Rainy Mood
Rainy Mood is the internet's most popular rain experience
$2.99 · In-app purchases
PRICE
$2.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.7
997 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.
Build your own version
Build Kit
Make this idea yours
A product spec, screen plans, and build steps for your coding agent.
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Combine features and design from your favorite apps.
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Make it yours Optional
What should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
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/
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 Rainy Mood: 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
Offer a wider variety of nature sounds and customizable soundscapes.
Assumption to check: Limited sound options compared to competitors
Validate with people who use this workflow before building.
Hypothesis 2
Implement social sharing and community features for users to share their favorite sounds.
Assumption to check: Lack of social features
Validate with people who use this workflow before building.
Hypothesis 3
Allow users to download sounds for offline listening.
Assumption to check: No offline access
Validate with people who use this workflow before building.
Hypothesis 4
Add a timer feature to automatically stop sounds after a set period.
Assumption to check: No timer functionality for sounds
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
Rainy Mood is the internet's most popular rain experience. Join millions of people who use Rainy Mood to help them sleep, study, and relax. The new Rainy Mood app has four fully-customizable rain scenes -- Classic, Ocean, Countryside, and Café. The world's #1 leader in rain sounds has painstakingly composed each rain soundscape. With stunning HD/48kHz 3D audio and algorithmic randomizer, your brain will naturally relax and focus. Our massive sample library includes 400+ unique thunder claps, cricket chirps, ocean waves, and special effects. Individual rain impact textures include rain on grass, dirt, wood, tin roof, ocean, leaves, and rocks. FEATURES + 3D audio, works with standard headphones + Algorithmic randomizer and massive sound library for always-fresh sound that never repeats + Sound mixer + Sleep timer + Energy efficient + Play your music simultaneously. Works with your music apps + Includes free lifetime updates.
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
expo-av
react-navigation
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.
