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
Castle Busters
SMASH EVERY CASTLE
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 4.6
85,578 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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Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for Castle Busters: 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
Introduce more characters with unique abilities and backgrounds.
Assumption to check: Limited character variety and depth.
Validate with people who use this workflow before building.
Hypothesis 2
Add new mechanics and challenges to keep gameplay fresh.
Assumption to check: Repetitive gameplay mechanics after a few levels.
Validate with people who use this workflow before building.
Hypothesis 3
Balance free and paid characters to enhance fair play.
Assumption to check: In-app purchases can feel pay-to-win.
Validate with people who use this workflow before building.
Hypothesis 4
Implement a more strategic ad placement system that aligns with gameplay.
Assumption to check: Ads can disrupt gameplay flow.
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
SMASH EVERY CASTLE. RULE EVERY ARENA. Castle Busters is fast, loud, and unfair in the best way. Every brick breaks. Every shot counts. Draft 8 units, load your keep, and turn your rival's castle into a pile of rubble before they do it to you first. No grinding waves of bots. No 20-minute matches. Just real-time 1v1 PvP where one good angle wins the war. DESTROY THE WALLS, NOT THE CLOCK Matches are quick. Decisions are not. Pick your shot, read the enemy line, and fire. Every wall, tower and turret is destructible, so the map is never the same twice. Collapse a floor under an archer. Carve your own path, literally. DRAFT YOUR SQUAD Wrecker, Napalmer, Bomber, Scout, Fairy, Crow... Pick any 8. Each unit changes how you play, what angles you attack, and how you defend. Some builds are patient. Some are chaos. None of them are wrong if they win. FORTIFY THE KEEP Your castle is your army's home, shield, and weapon. Reinforce the walls that matter. Leave decoys. Bait your rival into breaking through somewhere they shouldn't. Defense isn't passive here, it's a trap. THE FORGE Upgrade your units. Strengthen your keep. Unlock new arenas with new hazards, new obstacles, new ways to break things. The deeper you go, the meaner the meta gets. CLIMB THE LADDER Climb your away towards Clash Colosseum. Arena by arena. Seasonal leaderboards. Rank matches against players who want your crown as badly as you want theirs. Only one castle stays standing. Sharpen your aim. Stack your squad. Crack their keep. The arena is open. Go break something. Castle Busters is free to download and play. Some items are available for purchase with real money. A network connection is required. You must be at least 13 years old to play.
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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
React Navigation
Zustand
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.
