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
Arm Care
The ArmCare App is designed to be used with the ArmCare Strength Sensor
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 4.9
2,908 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 included17 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 Arm Care: map the core Sports 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
Expand the exercise library with user-generated content.
Assumption to check: Limited exercise variety
Validate with people who use this workflow before building.
Hypothesis 2
Introduce forums or community challenges.
Assumption to check: No community features
Validate with people who use this workflow before building.
Hypothesis 3
Simplify pricing tiers and clarify benefits.
Assumption to check: Subscription model can be confusing
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
The ArmCare App is designed to be used with the ArmCare Strength Sensor. ArmCare Technology uses your strength, fatigue and recovery data to individualize training and unlock the potential for huge velocity gains. Gone are the days of using the same arm care band routine. The future is knowing where you are weak, how your arm fatigues and if you are recovering optimally between outings. Thousands of players and over 20 MLB teams are using the ArmCare technology to monitor arm health and velocity. HOW IT WORKS 1. MEASURE YOUR STRENGTH Using the ArmCare Sensor, accurately measure the strength & range of motion of your arm in 5 minutes…with no assistance needed. 2. CHECK YOUR KEY METRICS Strength, Fatigue, Recovery are used to individualize throwing programs, bullpens, pitch counts, velocity programs, pitch design & mechanics 3. ARMCARE OPTIMIZED FOR YOU The app prescribes customized arm care programs to attack your weak links. You know exactly what training to do to get results fast BENEFITS - Players will get real metrics on their rotator cuff strength the same way a bat sensor helps dial in swing path and launch angle. - Players will receive custom arm care programs everyday to help strengthen their weak links, rather than a one size fits all program. - Each player will know exactly what to do to keep his arm feeling fresh and strong all season long. No Medical Advice: - The Program provides general information only and does not constitute providing medical or health care services of any kind, nor engagement in human subjects research. - The information provided in the Program is not medical advice and should not be treated as such. Arm Care subscription Premium: Arm Care plans: Annual: $72 Payments and Renewal: Payment will be charged to iTunes Account at confirmation of purchase. Subscription automatically renews unless auto-renew is turned off at least 24-hours before the end of the current period. Account will be charged for renewal within 24-hours prior to the end of the current period. You can manage or turn off auto-renew in your Account settings at any time after purchase. No cancellation of the current subscription is allowed during the active period. Terms of use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/ Privacy policy: https://armcare.com/pages/privacy-policy
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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.
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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.
