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
ThriftBooks: New & Used Books
Shop 13 million new and used books at up to 90% off list price
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 3.8
1,556 ratings · Top 50%
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 included17 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 ThriftBooks: New & Used Books: 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
Implement real-time inventory tracking and notifications.
Assumption to check: Limited book availability and stock issues
Validate with people who use this workflow before building.
Hypothesis 2
Enhance search with filters and sorting options.
Assumption to check: Poor search functionality
Validate with people who use this workflow before building.
Hypothesis 3
Simplify navigation and improve visual hierarchy.
Assumption to check: Confusing user interface
Validate with people who use this workflow before building.
Hypothesis 4
Optimize images and reduce data fetching delays.
Assumption to check: Slow loading times
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
Shop 13 million new and used books at up to 90% off list price. The ThriftBooks app lets book lovers quickly and easily search, browse, get book details, and buy millions of books, textbooks, and graphic novels. Scan bar codes to compare prices and check availability to make sure you get the best book prices. Shop ThriftBooks Deals to get 10% off on more than 150,000 items every day. Join ReadingRewards to earn a FREE BOOK for every 500 points you earn. See personalized recommendations based on your interests and get an instant email notification when we receive an item on your wish list. About ThriftBooks • Over 300,000 TrustPilot reviews with a 4.7/5 TrustScore • 100% Satisfaction Guarantee Benefits: • Get an instant notification when we receive an out-of-stock item on your wish list • Find the best book prices using the bar code scanner to check real-time prices and inventory • Get free US shipping on orders over $15 in 100% recyclable packaging • See personalized recommendations based on your interests • Sign in using your existing ThriftBooks account to access your saved wish lists, payment methods, and shipping addresses • Receive exclusive deals and offers Features: • Bar Code Scanner: Compare prices and check inventory • Everyday Deals: 10% off more than 150,000 titles with ThriftBooks Deals • ReadingRewards: Earn FREE BOOKS for reading, shopping, and other activities • Special Formats: Large print, foreign language, and audiobooks • Collectible Books: Treasured first editions, signed copies, and out-of-print titles at reasonable prices • What’s Trending: See the hottest books Shop bestsellers from the latest new releases to all-time favorites from a broad range of categories, including: • Arts, Music & Entertainment • Biographies & Memoirs • Business & Investing • Children’s Books • Classics • Cookbooks • Gay and Lesbian • Health, Fitness & Dieting • History • Literature & Popular Fiction • Mystery, Thriller & Suspense • Rare & Collectible Books • Religion & Spirituality • Romance • Sci-Fi & Fantasy • Self-Help • Teen & Young Adult
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
Supabase
Zustand
React Navigation
Axios
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.
