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
Music Speed Changer
Change your music's tempo and pitch in realtime quick and easy
$2.99 · In-app purchases
PRICE
$2.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 3.3
16 ratings · Below Average
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 included14 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 Music Speed Changer: 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
Support more audio formats and cloud services.
Assumption to check: Limited audio file support
Validate with people who use this workflow before building.
Hypothesis 2
Implement a modern UI with better visual feedback.
Assumption to check: User interface can feel outdated
Validate with people who use this workflow before building.
Hypothesis 3
Enhance audio playback stability and quality.
Assumption to check: Inconsistent playback performance
Validate with people who use this workflow before building.
Hypothesis 4
Introduce sharing options for tracks and speed settings.
Assumption to check: Lack of social features
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
Change your music's tempo and pitch in realtime quick and easy. Just select an audio file, mark the region you want to play (and loop/repeat) and change tempo and pitch on the fly. It is also possible to export the changed audio file. Use cases of Music Speed Changer are for instance: practicing guitar and other music instruments, transcriptions, change the speed of audiobooks... Features: - Change pitch and tempo (speed, time-stretch) independently - Loop region - Select region - Filtering - Import various formats including mp3, wav, m4a, ogg, aac, ... - Export to wav and mp3 - Volume amplification - Voice reduction - Separate playing of left/right channels - Import audio files from other apps to MSC - Import from Dropbox *NEW* - Send files by email *NEW* APS Player: http://www.tequnique.com/apsplayer Note: - Extreme pitch and tempo changes (for instance 24 semi-tones, which is quite a lot!) can lead to noise. - Voice reduction quality depends on the input. It works best with little compressed music and assumes that voice was recorded in mono and later mixed into the stereo channels (which is the case for a lot of music recordings)
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
expo-file-system
BUILD KIT DIFFICULTY
Advanced
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.
