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
MP3 Converter - Audio Trimmer
Join Millions of Happy Users! As an all-in-one audio toolkit, MP3 Converter is trusted by millions of users worldwide who rely on its powerful features every day
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 4.7
29,424 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 included18 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 MP3 Converter - Audio Trimmer: 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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App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
Screenshots
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App Store description
Join Millions of Happy Users! As an all-in-one audio toolkit, MP3 Converter is trusted by millions of users worldwide who rely on its powerful features every day. Whether you're converting files, creating custom ringtones, or fine-tuning your music, everything you need is just a tap away. With an intuitive, user-friendly interface, anyone can start using it right away — no experience required. It's the go-to tool for enhancing your music experience on the go. [MP3 Converter] Easily convert any audio or video file to high-quality MP3 format. Whether it's a favorite song or a video clip, our app delivers a smooth, fast conversion process, giving you portable music anytime, anywhere. Fine-tune your output with customization options like bitrate, sample rate, and audio quality to suit your exact needs. [Ringtone Maker] Extract audio from TikTok, YouTube, Instagram, and other top platforms — catchy snippets, background laughs, viral sounds — and turn them into ringtones. You can also download your favorite songs, then trim and refine the exact part you love to create a one-of-a-kind ringtone that matches your style. [Video to MP3] Extract audio from any video in seconds — MP4, AVI, or MOV, whatever you have. With just a few taps, your videos become high-quality MP3 files you can save to your device, share with friends, or listen to on the go without ever watching the video. Multiple audio quality options let you pick what works best for you. [Audio Trimmer] A complete toolkit for editing and refining your sound. Adjust volume, apply filters, and fine-tune pitch and tempo for precise control. Cut and trim any segment with exact start/end points, then add fade-in/out effects to create custom ringtones, alarms, and music clips — or blend multiple tracks into one seamless song. With batch editing, you can polish several files at once, so every sound comes out just the way you want it. [Free Music] Stream a wide range of free music tracks — Browse genres, discover new tunes to suit your mood, and enjoy them all at your fingertips. [Offline Music] No internet? No problem. Enjoy your music offline anytime — on the go, traveling, or in areas without Wi-Fi. Download tracks and listen without interruptions. [Song Finder] Search, discover, and play music, podcasts, and audiobooks from around the world. Subscription Information: Premium Access：Unlock unlimited audio conversion, ringtone setting, and audio trimming. Plans：Weekly, monthly, and annual subscription options available. Auto-Renewal：Payment is charged to your iTunes Account upon confirmation. Subscriptions auto-renew unless canceled 24 hours before the current period ends. Management：Manage your subscription and disable auto-renewal in your Account Settings after purchase. Thank you for choosing our MP3 Converter! If you have any questions, feedback, or need assistance, feel free to reach out to our support team. Link to the Terms of Use (EULA) : http://markwatermark.com/license_agreement.html Link to the Privacy Policy : http://markwatermark.com/mp3_privacy.html
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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
Offer more free conversions or a generous trial period.
Assumption to check: Limited free conversions before paywall.
Validate with people who use this workflow before building.
Hypothesis 2
Expand the range of supported audio formats.
Assumption to check: File format support may be restricted.
Validate with people who use this workflow before building.
Hypothesis 3
Simplify the onboarding process and provide tutorials.
Assumption to check: User interface can be confusing for new users.
Validate with people who use this workflow before building.
Hypothesis 4
Optimize conversion algorithms for faster processing.
Assumption to check: Conversion speed may vary significantly.
Validate with people who use this workflow before building.
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
React Navigation
Axios
SQLite
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.
