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
Hilda Synthesizer
Hilda is a Complex Oscillator Monosynth, inspired by the most interesting aspects of both west-coast and east-coast synthesis techniques
$12.99 · In-app purchases
PRICE
$12.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.9
57 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 included16 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 Hilda Synthesizer: 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
Include a wider variety of sound presets and customizable options.
Assumption to check: Limited sound options compared to larger synthesizer apps
Validate with people who use this workflow before building.
Hypothesis 2
Implement a tutorial or guided onboarding process.
Assumption to check: Steep learning curve for new users
Validate with people who use this workflow before building.
Hypothesis 3
Add social sharing features to allow users to share their creations.
Assumption to check: Lack of social features for sharing sounds
Validate with people who use this workflow before building.
Hypothesis 4
Enable offline sound playback and editing capabilities.
Assumption to check: No offline functionality
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
Hilda is a Complex Oscillator Monosynth, inspired by the most interesting aspects of both west-coast and east-coast synthesis techniques. You'll find a wave folder, lowpass gate, and audio-rate modulations, but also a 12-mode filter and traditional VCA circuit. All parts of the instrument are carefully circuit-modelled to sound as analog (or digital, where applicable) as possible. It's like a best-of-all-worlds semi modular synth, but without the patch cables. The unique mix of different synthesis components adds up to a unique sounding electronic instrument, which can be used as a playable synthesizer, a MIDI sequencer and an audio effect for external audio - or any combination of those three. - Full Audio Unit compatibility (AUv3 instrument, audio effect and MIDI processor modes supported) - Universal design (iPhone and iPad; iPad Air 2 or higher recommended) - Built-in analog style 16 Step MIDI Sequencer with custom scales - 12 mode filter, based on the Oberheim Xpander design - Drone mode lets you [partially] bypass the VCA/LPG and just go with the flow - DIY Lo-Fi digital delay circuit emulation - Live pads with effects that can be triggered via the UI (or via exposed AU Parameters) - All synth settings exposed a AU Parameters (for automation and MIDI learning in your host of choice) - MIDI Processor plugin mode disables synth to save CPU - Carefully handcrafted by yours truly, to capture the essence of my love for tinkering and experimenting with sound :-) Find the user manual on ruismaker.com
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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
@supabase/supabase-js
zustand
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.
