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
Fart Sounds
Downloaded over 1 million times, Fart Sounds is the original and leading fart app worldwide
$1.99 · In-app purchases
PRICE
$1.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 3.5
4 ratings · Top 50%
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
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A product spec, screen plans, and build steps for your coding agent.
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What should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
What's included14 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 Fart Sounds: map the core Entertainment 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
Introduce a wider range of high-quality sounds and categories.
Assumption to check: Limited sound variety and quality
Validate with people who use this workflow before building.
Hypothesis 2
Modernize the UI with animations and fresh design.
Assumption to check: User interface feels outdated
Validate with people who use this workflow before building.
Hypothesis 3
Add functionality to share sounds on social media.
Assumption to check: No social sharing features
Validate with people who use this workflow before building.
Hypothesis 4
Improve UI/UX for subscription and restore purchases.
Assumption to check: In-app purchase process is 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
Downloaded over 1 million times, Fart Sounds is the original and leading fart app worldwide. The name says it all. This is the real deal. No banners, no ads, no getting spam'd; just pure fart fun. It was even used on Conan O'Brien's show on TBS to create one of their segments. These 27 farts will make you laugh, cry, and hopefully embarrass a few people. Don’t accept any substitutes. This is a great tool; with everything from the interface to the sounds being made for the true fart prankster. Each sound was meticulously remastered to cut out any background noises and made to be crystal clear. Other apps will throw in a few sounds littered with ugly background noises that aren’t true to the clarity of a real fart. There is a “Help” page with easy to read instructions, as well as an email address for technical support and feedback. We promptly answer support requests and listen to any recommendations to help make this app even better!
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-navigation
expo-av
react-native-async-storage
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.
