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
Barbell Loader and Calculator
Developed by an olympic weightlifter, Barbell Loader is for anyone who would rather focus on lifting, not math.
$2.99 · In-app purchases
PRICE
$2.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.9
142 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/
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 Barbell Loader and Calculator: 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
Include a feature for users to add and save custom exercises.
Assumption to check: Limited exercise database, making it hard to customize workouts
Validate with people who use this workflow before building.
Hypothesis 2
Implement a progress tracking feature with graphs and statistics.
Assumption to check: Difficult to track progress over time
Validate with people who use this workflow before building.
Hypothesis 3
Make the purchasing options more transparent with clear descriptions.
Assumption to check: In-app purchase notifications are unclear
Validate with people who use this workflow before building.
Hypothesis 4
Allow users to share their workout results on social media.
Assumption to check: No social sharing options
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
Developed by an olympic weightlifter, Barbell Loader is for anyone who would rather focus on lifting, not math. Barbell Loader and Calculator is for: -Weightlifting -Powerlifting -Bodybuilding -CrossFit and everyone else who lifts weights. This app is perfect for saving time at Weightlifting and Powerlifting competitions! Features BARBELL LOADER -Load: Click on the plate buttons to load the bar yourself. -Calculate: Type in a weight, and Barbell Loader will load the bar with either official IWF/IPF-colored kilogram plates or standard pound plates. -Convert: Every weight is automatically converted between pounds and kilograms. PERCENTAGES CALCULATOR -Every weight has percentages calculated automatically that you can then load onto the bar. SINCLAIR AND WILKS CALCULATOR -Enter 2 out of 3 fields and the Calculator will resolve the third. -For example, if you enter your Total Weight Lifted and Sinclair Score, the Calculator will tell you the Bodyweight needed. REP MAX CALCULATOR -Enter just the weight lifted and the repetitions and the Calculator will resolve everything from you 1 Rep Max to 10 Rep Max. LOG -Click a button, and Barbell Loader will log the current weight and time into a notepad that you can edit further. ALSO: -Customize your plate inventory. -On/off switch for competition 2.5 kg collars. -Set your bar weight. -Create your own custom plates. -Optimize the weight on the bar. -Remove plates one at a time as necessary. -And more!
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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
Supabase
react-native-reanimated
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.
