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
Umamusume: Pretty Derby
Umamusume: Pretty Derby is ready to race! Scout featured trainees and supporters as you navigate the immersive sports life simulation through the game's in-depth training system and top-of-the-line 3D graphics!
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 4.6
4,779 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.
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 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 Umamusume: Pretty Derby: 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
Allow deeper customization and personalization of characters.
Assumption to check: Limited character customization options
Validate with people who use this workflow before building.
Hypothesis 2
Introduce more varied gameplay modes to keep users engaged.
Assumption to check: Repetitive gameplay mechanics
Validate with people who use this workflow before building.
Hypothesis 3
Provide more free content or earning options to balance in-app purchases.
Assumption to check: In-app purchase pressure
Validate with people who use this workflow before building.
Hypothesis 4
Optimize app performance for a smoother experience on lower-end devices.
Assumption to check: Performance issues 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
Umamusume: Pretty Derby is ready to race! Scout featured trainees and supporters as you navigate the immersive sports life simulation through the game's in-depth training system and top-of-the-line 3D graphics! Introduction -- Umamusume. They are born to run. They inherit otherworldly names, and are inspirited by dreams most dramatic and wonderful. Now, they run ever forward. That, is their destiny. No one knows how the races that lie in their futures will end. Even so, they continue to run, aiming only toward the goal in front of them. -- Each and every one of the runners sports a unique charm. It's up to you, the trainer, to lead them down the path of victory! You have but one goal—raise your Umamusume to her fullest potential and help turn her greatest dreams into reality. In order to reach these newfound heights, it's your job to participate in—and win—as many races as possible! Triumph awaits those who train hard and work to communicate. Only by cooperating will you take the crown! -- Experience the thrilling stories of historic racers, such as: Special Week (Voice: Azumi Waki) Silence Suzuka (Voice: Marika Kohno) Tokai Teio (Voice: Machico) Oguri Cap (Voice: Tomoyo Takayanagi) Gold Ship (Voice: Hitomi Ueda) Vodka (Voice: Ayaka Ohashi) Daiwa Scarlet (Voice: Chisa Kimura) Mejiro McQueen (Voice: Saori Onishi) Symboli Rudolf (Voice: Azusa Tadokoro) Rice Shower (Voice: Manaka Iwami) Haru Urara (Voice: Yukina Shuto) Nice Nature (Voice: Kaori Maeda) ...and so many more—over 20 Umamusume are searching for a trainer to help them achieve their goals! -- Cheer for your favorite Umamusume and immerse yourself in exhilarating races and stunning performances in breathtaking 3D graphics. Up to 18 Umamusume compete in races against each other for first place—watch them go as you tune in to the game's incredibly realistic live commentary. And of course, stick around after the race to support the victor during a dazzling winning concert! Whether on the racetrack or the stage, raise the roof to each exciting new performance! -- Follow us on X: https://x.com/umamusume_eng -- For more information, check out our official website: https://umamusume.com/ -- Recommended Devices iOS 14.0 or later: - iPhone 15, 15 Plus, 15 Pro, 15 Pro Max - iPhone 14, 14 Plus, 14 Pro, 14 Pro Max - iPhone 13, 13 mini, 13 Pro, 13 Pro Max - iPhone 12, 12 mini, 12 Pro, 12 Pro Max - iPhone 11, 11 Pro, 11 Pro Max - iPhone X, Xs, Xs Max, XR iPadOS 15.0 or later: - iPad (7th, 8th, 9th, 10th generation) - iPad mini (5th, 6th generation) - iPad Air (3rd, 4th, 5th generation) - iPad Pro 11-inch (1st, 2nd, 3rd, 4th generation) - iPad Pro 12.9-inch (3rd, 4th, 5th, 6th generation)
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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
TypeScript
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.
