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
Julianator
This app converts a date between Julian Day of Year and Gregorian
$0.99 · In-app purchases
PRICE
$0.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.7
114 ratings · Top 15%
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 included18 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 Julianator: 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
Allow users to customize the display formats for dates.
Assumption to check: Limited customization options for the date formats.
Validate with people who use this workflow before building.
Hypothesis 2
Implement multilingual support for broader reach.
Assumption to check: No support for multiple languages.
Validate with people who use this workflow before building.
Hypothesis 3
Add options to share conversion results on social media.
Assumption to check: Lack of social sharing features.
Validate with people who use this workflow before building.
Hypothesis 4
Create home screen widgets to provide quick conversion access.
Assumption to check: No widget support for quick access.
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
This app converts a date between Julian Day of Year and Gregorian. For example, September 11, 2022 converts to 2022-254 and 2022-254 converts to September 11, 2022. This app will convert both directions. Julian Date for this app refers to the day-of-year number (more properly, the ordinal date) in the Gregorian calendar, often used in mainframe computer systems, the military, and the food industry. (Note: this app does not used the term Julian Date to refer to the astronomy definition which is calculated from 4713 BC) Features a simple clean interface with pickers for the dates. The app also features a monthly view allowing a quick view of both Gregorian and Julian days for the entire month. Widgets are available for both the Home Screen and the Lock Screen to display the current day of year. A Watch app is available that includes a date converter and complications to display the current day of year. Note: The app's icon does not change to reflect the current day. Privacy Policy: https://julianator.brightdaydigital.com/privacy Terms of Service: https://julianator.brightdaydigital.com/terms
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
expo-date-picker
react-native-clipboard
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.
