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
HarpNinja Diatonic Harmonica
HarpNinja - Learn harmonica faster!
$19.99 · In-app purchases
PRICE
$19.99
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/
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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 HarpNinja Diatonic Harmonica: 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
Incorporate more gamification elements to enhance engagement.
Assumption to check: Limited interactive features compared to other music apps
Validate with people who use this workflow before building.
Hypothesis 2
Allow users to download lessons for offline practice.
Assumption to check: No offline access to lessons
Validate with people who use this workflow before building.
Hypothesis 3
Offer a freemium model with basic lessons available for free.
Assumption to check: High price point for a niche audience
Validate with people who use this workflow before building.
Hypothesis 4
Integrate social sharing options to increase community interaction.
Assumption to check: Lack of social features for sharing progress
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
HarpNinja - Learn harmonica faster! Pitch recognition + easy music theory HarpNinja Diatonic Harmonica is a diatonic harmonica version of its big brother app HarpNinja. It includes just the essential tuning and music theory features for easy access on your smartphone or tablet wherever you may be. The user interface is designed to scale from small smartphones (5"++ recommended minimum) to tablets and to desktops. *** Reviews of HarpNinja: 1. Bluesharmonica.com http://www.bluesharmonica.com/harpninja 2. Bluestime.it http://www.bluestime.it/harpninja.html Please Note: HarpNinja Diatonic Harmonica RECOMMENDED MINIMUM SCREEN SIZE would be at least a 5" screen smartphone. Anything below this size would really be too small to be useful. If you have technical issues please contact me direct or via the support forum. HarpNinja supports your harmonica learning independent of whatever method you are using. It has two modes. Real time pitch recognition shows you what you play. Harmonica mode is where you can visualize all the notes on a diatonic (10-hole) harmonica. Select from 8 commonly available Diatonic tunings (Major, Natural Minor, Harmonic Minor, Melody maker, Country, Diminished, Powerbender, or Suzuki Ultrabend Sub30) or 7 Chromatic Tunings (Standard/Solo, Bebop, C6, C6 Bebop, Diminished, Augmented, or Whole Tone), all 12 Keys, 18 Scales, and 5 Chord types (Maj, Min, 7th, Aug, Dim). You can also switch the display between notes or music intervals. Play your harmonica and the Real time pitch recognition highlights the notes on screen. An audio recorder also allows you to record up to 30 second segments to hear your own playing. Interactive Circle of Fifths makes music theory easy. Circle of Fifths mode is an interactive Circle of Fifth’s specially adapted for harmonica. The Circle of Fifth’s is a well known music theory tool for working out chord and scale relationships. Settings mode is where you can adjust all the harmonica and application settings, in addition to checking the integrated news feed and any errors. Please see the website help and tutorials for more guidance: http://www.harpninja.com/wp/faqhelp/ http://www.harpninja.com/wp/video-help/
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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
Axios
React Navigation
Expo AV
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.
