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
E85 Mix Ethanol Calculator
The app is smart and it will remember your tank capacity and target ethanol mix values so next time you want to see how much E85 you need to add to get your target ethanol mix, you will only have to specify your curre...
$1.99 · In-app purchases
PRICE
$1.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 3.1
7 ratings · Below Average
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 included16 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 E85 Mix Ethanol 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 tips for users
Assumption to check: Limited features compared to competitors
Validate with people who use this workflow before building.
Hypothesis 2
Redesign UI for better clarity and ease of use
Assumption to check: User interface can be confusing
Validate with people who use this workflow before building.
Hypothesis 3
Implement a help section or FAQ
Assumption to check: Lack of customer support options
Validate with people who use this workflow before building.
Hypothesis 4
Provide more valuable content for users after purchase
Assumption to check: In-app purchase limitations
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 app is smart and it will remember your tank capacity and target ethanol mix values so next time you want to see how much E85 you need to add to get your target ethanol mix, you will only have to specify your current tank percentage. This way it is the fastest method to calculate how much gas and e85 you need to put in the tank. It is such a fast method, by the time you get out of your car, you already know how much fuel you need to add in the tank. Literally 3 seconds. Additional Information: You have the option to select what your current ethanol content is if you measured it with an ethanol content analyzer and the app easily calculates how much E85 and how much gas you need to add to reach your target ethanol mix. You can also specify the ethanol content of your E85 if you measured it with an Ethanol Content Analyzer, so this way you get an exact guide as to how much E85 and how much gas you have to put in the tank. Tank Capacity -Specify the capacity of your tank Tank Percentage -How full is your tank E85 Ethanol Content -What is the Ethanol content of your E85 what you are about to put in the tank Target Ethanol Mix -What your desired ethanol mix is, for example (E30 E40 E50 E60 E85) Current Ethanol Mix -What your current ethanol percentage is of your current fuel in the tank For any questions please feel free to contact at [email protected]
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 Native
Expo
React Navigation
react-native-clipboard
expo-sharing
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.
