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
BookBub
Discover amazing deals on bestselling ebooks, plus hundreds of free ebooks
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 4.7
959 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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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 BookBub: map the core Books 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 their book recommendations based on preferences.
Assumption to check: Limited personalization options for users.
Validate with people who use this workflow before building.
Hypothesis 2
Implement a more straightforward subscription management interface.
Assumption to check: Difficulties in managing subscriptions.
Validate with people who use this workflow before building.
Hypothesis 3
Enhance reliability and user feedback during deal claiming.
Assumption to check: Occasional bugs in deal claiming process.
Validate with people who use this workflow before building.
Hypothesis 4
Introduce features for users to share their favorite books with friends.
Assumption to check: Lack of social features for sharing books.
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
Discover amazing deals on bestselling ebooks, plus hundreds of free ebooks. Track your wishlist and get alerts when your most wanted titles go on sale. BookBub helps millions of readers save money on ebooks they'll love. Our expert editors hand pick incredible ebook deals every day across all major genres — romance, mystery, thrillers, women's fiction, fantasy, contemporary fiction, nonfiction, and many more — from bestselling authors to hidden gems. WHY READERS LOVE BOOKBUB: THE BIGGEST EBOOKS, UP TO 95% OFF We feature limited-time ebook deals from all major retailers. Get huge savings on the biggest books and authors, including #1 New York Times bestsellers. HUNDREDS OF FREE EBOOKS Unlock a vast selection of free ebooks across 40+ genres, with new titles added each day YOUR PERSONAL BOOK TRACKER Build your reading wishlist and never miss a sale. Add any book you want to read, and we'll notify you when it's discounted. Track your TBR (to-be-read) list, sort by release date or author, and mark it as read when you're done. PERSONALIZED TO YOUR READING TASTE Our editorial team hand picks from thousands of ebooks to bring you only the best — from BookTok favorites to award-winning fiction. FEATURES: - Browse daily ebook deals personalized to your reading preferences - Track unlimited books on your wishlist - Get price alerts for specific titles or favorite authors - Discover popular titles to add to your list - Filter deals by genre and price - Buy from your favorite ebook store "When we say 'deal,' we mean it — many of BookBub's titles are free entirely, $0.99, or just a couple of bucks." — Lifehacker "Bargain-basement deals on ebooks." — The New York Times Join millions of happy readers saving money on ebooks every day. Questions? Visit bookbub.com/apphelp
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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
Supabase
Redux
React Navigation
BUILD KIT DIFFICULTY
Advanced
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.
