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
LINE
LINE is transforming the way people communicate, closing the distance between family, friends, and loved ones—for free
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 3.2
18,329 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 included19 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 LINE: map the core Social Networking 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 voice and video calling, and enhanced group features.
Assumption to check: Limited features compared to competitors like WhatsApp and Telegram.
Validate with people who use this workflow before building.
Hypothesis 2
Implement more thorough testing and stability improvements.
Assumption to check: Frequent crashes and bugs reported by users.
Validate with people who use this workflow before building.
Hypothesis 3
Simplify the UI and improve user onboarding.
Assumption to check: User interface can be cluttered and confusing.
Validate with people who use this workflow before building.
Hypothesis 4
Provide transparent pricing and clearer explanations of benefits.
Assumption to check: In-app purchases can be confusing and not well explained.
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
LINE is transforming the way people communicate, closing the distance between family, friends, and loved ones—for free. With voice and video calls, messages, and a limitless variety of exciting stickers, you’ll be able to express yourself in ways that you never thought possible. Available all around the world on mobile, desktop, and Apple Watch, the LINE platform continues to grow, always offering new services and features that make your life more fun and convenient. ◆ Messages, Voice calls, Video calls. Enjoy voice and video calls and exchanging messages with your LINE friends. ◆ LINE stickers, emojis, and themes Express yourself just the way you want with stickers and emojis. Also, find your favorite themes to customize your LINE app. ◆ Home Gives you easy access to your friends list, birthdays, the sticker shop and various services and contents offered by LINE. ◆ LINE VOOM Available in Japan, Taiwan, and Thailand, you can explore even more content that you may like in the "For you" tab. ◆ Seamless connection on mobile, Apple Watch, and desktop Chat anytime and anywhere. Whether you’re on the go or working at the office or remotely, use LINE via your iPhone, Apple Watch, or desktop. ◆ Store your personal information with Keep Memo My own chatroom to temporarily store messages, photos, and videos. ◆ Messages protected with Letter Sealing Letter Sealing encrypts your messages, call history and location information. Always be assured of your privacy when using LINE. *We recommend using a data plan or connecting to Wi-Fi as you may incur data usage fees otherwise. *Please check the recommended specifications from LINE settings > “Help center” > “LINE usage environment/Settings” > "System requirements for LINE” when installing/updating the LINE app. In addition, if you're using an old version of iOS, we recommend updating it to the latest version. ▼Click here to see how to update your iOS version. https://support.apple.com/en-us/HT204204 ********** If your network speed is too slow or you don't have enough device storage, LINE may not install properly. If this happens, please check your connection and try again. **********
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.
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BUILD KIT DIFFICULTY
Expert
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.
