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
Fuel Calculator: MPG, L100k
The Fuel Calculator app is a tool to help you save money and time by calculating fuel expenditure cost and efficiency as either MPG or L/100km.
$0.99 · In-app purchases
PRICE
$0.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 5.0
2 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
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A product spec, screen plans, and build steps for your coding agent.
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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 Fuel Calculator: MPG, L100k: map the core Business 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 support for additional metrics like cost per mile or trip cost.
Assumption to check: Limited calculation methods (only MPG and L/100km)
Validate with people who use this workflow before building.
Hypothesis 2
Implement cloud storage for user data to access calculations on multiple devices.
Assumption to check: No syncing across devices
Validate with people who use this workflow before building.
Hypothesis 3
Enhance UI with dark mode and customizable themes.
Assumption to check: Basic UI with little customization
Validate with people who use this workflow before building.
Hypothesis 4
Add functionality to share results via social media or messaging.
Assumption to check: No sharing options for results
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 Fuel Calculator app is a tool to help you save money and time by calculating fuel expenditure cost and efficiency as either MPG or L/100km. Calculators • Fuel Consumption Calculator • Fuel Cost & Max Distance • Relative Fuel Cost Difference • Odometer Difference Calc • Odometer - Total Fuel Cost • Odometer - Fuel per Unit Cost Area Converters • Inches & Centi- & Millimeters • Feet & Yards & Meters Distance Converters • Feet & Yards & Meters • Miles & Kilometers Volume Converters • Gallons to Liters • Liters to Gallons • Cubic Inches & Centimeters This app features: • Send your calculations or conversions by email • Universal App (iPhone and iPad) • Fast app switching • Automatically Saves Your Inputs • Latest version of iOS is supported • All iPhone screens and the original 3.5 inch screen are supported No network connectivity required.
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.
SUGGESTED BUILD STACK
React Navigation
Formik
Yup
Axios
Expo
Zustand
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.
