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
The Binding of Isaac: Rebirth
"When Isaac’s mother starts hearing the voice of God demanding a sacrifice be made to prove her faith, Isaac escapes into the basement, where he faces droves of deranged enemies, lost brothers and sisters, his fears a...
$14.99 · In-app purchases
OVERALL US RANK
#92
Paid · all categories
REVENUE (Est)
$120K/mo
$66K - $175K
RATING
★ 4.5
4,225 ratings · Top 15%
Evidence scope: #92 is the current overall US Paid chart position. Category-chart positions shown in discovery are a separate scope. Revenue is a directional model estimate, not verified earnings.
Build your own version
Build Kit
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A product spec, screen plans, and build steps for your coding agent.
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What should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
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/
Preview a sample Build Kit No email needed
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 The Binding of Isaac: Rebirth: map the core Games 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 tutorial mode to guide players through mechanics.
Assumption to check: Steep learning curve for new players
Validate with people who use this workflow before building.
Hypothesis 2
Implement diverse challenges and unlockable content.
Assumption to check: Repetitive gameplay after several runs
Validate with people who use this workflow before building.
Hypothesis 3
Add detailed item descriptions and effects for better understanding.
Assumption to check: Limited item descriptions
Validate with people who use this workflow before building.
Hypothesis 4
Optimize graphics and performance for lower-end devices.
Assumption to check: Inconsistent performance on older devices
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
"When Isaac’s mother starts hearing the voice of God demanding a sacrifice be made to prove her faith, Isaac escapes into the basement, where he faces droves of deranged enemies, lost brothers and sisters, his fears and eventually his mother. Gameplay The Binding of Isaac: Rebirth is the randomly generated action RPG shooter that started the new roguelike era. Following Isaac on his journey, players will find bizarre treasures that change Isaac’s form, giving him superhuman abilities and enabling him to battle droves of mysterious creatures, discover secrets and fight his way to safety. Key Features: Over 500 hours of gameplay 4 BILLION Seeded runs! 20 Challenge runs 450+ items Integrated controller support for popular control pads Analog directional movement and speed Tons of feature film-quality animated endings Over 100 specialized seeds 2-player local co-op Over 100 co-op characters Dynamic lighting, visual effects and art direction Multiple Save slots Poop physics! A bunch of achievements The ultimate roguelike Uber secrets including: 10 Playable Characters 100+ enemies Over 50 bosses Mystic Runes Upgradeable shops Rooms FULL OF POOP!"
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
@supabase/supabase-js
react-native-reanimated
BUILD KIT DIFFICULTY
Expert
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.
