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
Rassel - Pocket shaker
Rassel – Pocket Shaker transforms your iPhone to a shaken percussion instrument
$0.99 · In-app purchases
PRICE
$0.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.7
78 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 Rassel - Pocket shaker: map the core Music 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
Allow users to edit and mix sounds more extensively.
Assumption to check: Limited sound customization options
Validate with people who use this workflow before building.
Hypothesis 2
Introduce options to share custom sounds with friends or the community.
Assumption to check: No community sharing features
Validate with people who use this workflow before building.
Hypothesis 3
Add visual waveforms or animations to enhance user experience.
Assumption to check: Lack of visual feedback during sound playback
Validate with people who use this workflow before building.
Hypothesis 4
Clarify what features are available for free versus paid.
Assumption to check: In-app purchase confusion
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
Rassel – Pocket Shaker transforms your iPhone to a shaken percussion instrument. Just pick up the device and shake it. This initial version comes with four different instruments: Egg, Shaker, Tambourine and Bells. Just swipe the screen to change between them. Unlike similar apps, Rassel is based on a unique audio rendering engine that accounts for continuous velocity changes based on how the sampled instruments are agitated. The device’s gyroscope is directly mapped to this velocity which makes any movement sound the way a real instrument would. We’ve tried to fine-tune the app to be as lifelike as possible, both in sound and handling response. We think we got pretty close. Features: - Instruments: Egg, Shaker, Tambourine and Bells - Choose between loose, normal or tight setting - Loudness boost option
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
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zustand
expo-av
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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.
