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
BMX Gear Calculator
Many years ago at bmxultra.com we started to develop a gear chart and a gear calculator specifically for BMXers that could be used on the web, so no matter where you were, providing you had an internet connection and ...
$1.99 · In-app purchases
PRICE
$1.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 3.6
9 ratings · Top 50%
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 included12 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 BMX Gear 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
Add more advanced calculations or custom gear settings.
Assumption to check: Limited features for advanced users
Validate with people who use this workflow before building.
Hypothesis 2
Implement a modern and clean UI design.
Assumption to check: User interface feels outdated
Validate with people who use this workflow before building.
Hypothesis 3
Optimize performance for older iOS devices.
Assumption to check: Inconsistent performance on older devices
Validate with people who use this workflow before building.
Hypothesis 4
Provide an in-app tutorial or guidance for new users.
Assumption to check: Lack of detailed help or tutorials
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
Many years ago at bmxultra.com we started to develop a gear chart and a gear calculator specifically for BMXers that could be used on the web, so no matter where you were, providing you had an internet connection and a browser, you could access them. Of course over the years they have changed somewhat. Now the calculator produces an interactive gear chart, which sounds very complicated but couldn't be easier to use. Not only that though, the calculator can give you exact roll out for Tioga PowerBlock tires and many other popular tires. Since we use it a lot ourselves we are very proud of what we have been able to produce and how popular it is. Every now and then, while at some tracks we found that internet connections on the phone were very slow making the gear calculator a little difficult to use. It's been a long time coming but we finally have our first iPhone/iPad app, the BMX Gear Calculator - the BMX specific gear calculator that works anywhere, anytime - no internet connection required - compare multiple gears in a simple chart on the one screen - includes: Tires Listed Tioga PowerBlock 20×1.75 PowerBlock 20×1.60 PowerBlock 20×1.40 PowerBlock 20×1.95 PowerBlock 20×1 3/8 PowerBlock 20×1 1/8 PowerBlock 24×1.40 PowerBlock 24×1.60 PowerBlock 24×1.75 PowerBlock 24×2.1 Comp 3 20×1.75 Comp 3 20×1.50 Comp 3 20×1 3/8 Comp 3 20×1 1/8 Comp 3 24×1.75 Comp 3 25th 20×1.75 ITS Micro Knobby MK2 20×1.75 Micro Knobby MK2 20×1.50 Micro Knobby MK2 20×1 3/8 Micro Knobby MK2 20×1 1/8 Micro Knobby MK2 20×1 Micro Knobby MK2 24×1.75 Micro Knobby MK2 24×1.50 Micro Knobby MK2 24×1 3/8 Micro Knobby MK2 24×1 1/8 Micro Knobby MK2 24×1 Maxxis DTH 20×1 1/8 DTH 20×1 3/8 DTH 20×1.75 DTH 20×1.5 DTH 24×1.75 Torch 20×1.75 Torch 20×1.5 Holy Roller 20×1.75 Holy Roller 20×1 3/8 Holy Roller 20×1 1/8 Holy Roller 24×1.85 Alienation TCS R1 20×1.60 TCS F1 20×1.95 Differential 20×1.75 Graffiti TCS 20×1.85 Kenda Konversion 20×1.75 Konversion 20×1.65 Konversion 20×1.50 Konversion 24×1.75 Konversion 24×1.50 Kompact Folding 20×1.75 Kontact Folding 20×1.75 VeeRubber Speedster 20×1 3/8 Speedster 20×1 1/8 Speedster 20×1.50 Speedster 20×1.6 Speedster 20×1.75 MK3 Foldable 20×1 MK3 Foldable 20×1 1/8 MK3 Foldable 20×1 3/8 MK3 Foldable 20×1.50 MK3 Foldable 20×1.75 MK3 Foldable 24×1 MK3 Foldable 24×1 1/8 MK3 Foldable 24×1 3/8 MK3 Foldable 24×1.50 MK3 Foldable 24×1.75 MK3 Foldable 24×1.85 IRC Siren 20×1 1/8 Siren 20×1 3/8 Siren 20×1.50 Siren 20×1.75 Siren 24×1.75 Arisun XLR8 Foldable 20×1.50 XLR8 Foldable 20×1.75 XLR8 Foldable 20×1.95 XLR8 20×1 1/8 XLR8 20×1 3/8 XLR8 20×1.50 XLR8 20×1.75 XLR8 20×1.95 XLR8 24×1.75 And if your specific tire is not listed you have two options Generic sizes 16×1.75 18×1.75 20×1 1/8 20×1 3/8 20×1.50 20×1.75 24×1 1/8 24×1 3/8 24×1.75 Custom Measure up the outer diameter of your rear wheel and work out your rollout
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.
