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
HLL Artillery Calculator
Artillery calculator for Hell Let Loose
$0.99 · In-app purchases
PRICE
$0.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.8
188 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.
Build your own version
Build Kit
Make this idea yours
A product spec, screen plans, and build steps for your coding agent.
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Combine features and design from your favorite apps.
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Make it yours Optional
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 HLL Artillery Calculator: map the core Utilities 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
Provide a broader range of measurement unit options.
Assumption to check: Limited unit conversions available
Validate with people who use this workflow before building.
Hypothesis 2
Implement validation and testing for accuracy.
Assumption to check: Occasional calculation errors reported
Validate with people who use this workflow before building.
Hypothesis 3
Add sharing features for users to share results easily.
Assumption to check: No sharing options for results
Validate with people who use this workflow before building.
Hypothesis 4
Simplify the UI for better usability and focus.
Assumption to check: User interface can be cluttered
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
Artillery calculator for Hell Let Loose. Enter distance or use voice to get instant firing values and stay focused on the battlefield. HLL Artillery Calculator is a fast and intuitive tool designed specifically for Hell Let Loose players. Calculate artillery settings in seconds and hit your targets faster. KEY FEATURES: • Voice input — just speak your distance, no typing needed • Classic input — fast and familiar controls • Hands-free landscape mode for quick use in battle • Apple Watch support — access it right from your wrist • Customization options — make it yours Simple, fast, and distraction-free — exactly what you need during combat. IMPORTANT: As of Update 10 (1.0 version of the game), artillery cannons may have a random dispersion of up to 20 m. This is part of the game design and cannot be accounted for by the app. This app is not affiliated with Hell Let Loose, Black Matter Pty Ltd, or Team17 Group PLC.
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.
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BUILD KIT DIFFICULTY
Starter
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.
