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
Guitar Tuner - Simply Tune
World's #1 best-reviewed guitar tuner app!
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 4.8
103,933 ratings · Top 5%
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 Guitar Tuner - Simply Tune: 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
Implement better audio analysis algorithms for more precise tuning.
Assumption to check: Users report inaccuracies in tuning feedback.
Validate with people who use this workflow before building.
Hypothesis 2
Add support for more instruments and custom tunings.
Assumption to check: Limited instruments available for tuning.
Validate with people who use this workflow before building.
Hypothesis 3
Allow caching of settings and basic functionalities offline.
Assumption to check: No offline functionality.
Validate with people who use this workflow before building.
Hypothesis 4
Offer an ad-free subscription tier or one-time purchase option.
Assumption to check: In-app ads are intrusive.
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
World's #1 best-reviewed guitar tuner app! 100% free premium tuner with chords & songs With lots of different instruments to choose from, you can be tuning your guitar, bass or ukulele with fun and ease, so that it plays at perfect pitch. It's as easy as that. Tuning just got easier with the new lightweight guitar tuner app by Simply - Simply Tune. Get it now! From the creators of Simply Guitar. TUNING INSTRUCTIONS BY EXPERT MUSICIANS Learn how to adjust your strings safely and accurately. STEP-BY-STEP GUIDANCE Simply Tune tuner guides you through the tuning process step by step with easy-to-understand visuals, showing you in which order you need to pluck your strings & indicating if the string is tuned right, too high or too low. AUTO-TUNE MODE & MANUAL TUNE MODE The automatic tuner automatically detects the closest string to the played pitch & the manual tuner tells you how close you are to the string you choose. ESSENTIAL CHORD LIBRARY Learn & practice the chords of your favorite songs on the go. --- How Simply Tune works --- • Place your device in front of you • Follow the tuning instructions • Get instant tuning feedback with clear guidance on how to proceed --- We would love to hear from you --- Tell us about your experience with Simply Tune. We would love to hear your feedback and suggestions on how we can make your tuning experience even better. Let us know at [email protected] --- Good to know --- Simply Tune is created by Simply, developers of award-winning apps Simply Piano and Simply Guitar. Simply are experts in creating educational and fun music apps for learning to play quickly and easily. Recommended and used by tens of thousands of music teachers worldwide with over 1 million songs learned every week. Awards & Recognition: “Editors' Choice” by Apple SF Music Tech Summit Startup Innovators Challenge Winner Best Tool for Beginners, NAMM EMI Innovation Challenge Award --- Contact --- Have questions, feedback or suggestions? Reach out to us at [email protected] Privacy policy: https://www.hellosimply.com/legal/privacy Terms of use: https://www.hellosimply.com/legal/terms
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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
React Navigation
expo-av
expo-sensors
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.
