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
ETA Calculator
ETA Calculator is a simple offline navigation tool for seafarers.
$0.99 · In-app purchases
PRICE
$0.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
N/A
No ratings yet
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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Combine features and design from your favorite apps.
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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 included14 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 ETA Calculator: map the core Navigation 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 features like real-time traffic updates or route optimization.
Assumption to check: Limited functionality compared to competitors
Validate with people who use this workflow before building.
Hypothesis 2
Implement user profiles and history tracking.
Assumption to check: Lack of user engagement features
Validate with people who use this workflow before building.
Hypothesis 3
Enable users to share estimated times via social media or messaging.
Assumption to check: No sharing options for results
Validate with people who use this workflow before building.
Hypothesis 4
Allow users to customize their input preferences or save frequent routes.
Assumption to check: Minimal customization 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
ETA Calculator is a simple offline navigation tool for seafarers. It helps maritime professionals with voyage planning, passage scheduling, and time management at sea. Main Functions 1. Estimated Time of Arrival (ETA): Enter distance and vessel speed to calculate expected arrival time. 2. Required Speed: Enter distance and desired arrival time to calculate the necessary speed. 3. History of Calculations: All previous ETA and speed results are automatically saved for quick reference. Useful For: - Bridge watch officers - Masters and chief officers - Students and cadets in maritime training - Anyone involved in time-critical passage planning Features: - Works fully offline, no internet required - Fast, accurate results with a clear interface - Light & dark themes for day and night use - 24-hour time format, matching maritime standards ETA Calculator is designed for all vessel types and sizes — from training simulators to real-world navigation. Reliable, accurate, and easy to use.
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
Zustand
React Navigation
Async Storage
React Native Paper
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.
