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
Harry's LapTimer Petrolhead
Harry's LapTimer is the advanced tool for car enthusiast
$19.99 · In-app purchases
PRICE
$19.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 3.8
153 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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Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for Harry's LapTimer Petrolhead: map the core Sports 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 a more intuitive navigation system with clearer labels.
Assumption to check: Users report difficulty in navigating between sessions and stats.
Validate with people who use this workflow before building.
Hypothesis 2
Enhance sharing functionality to include social media and messaging.
Assumption to check: Limited sharing options for lap times.
Validate with people who use this workflow before building.
Hypothesis 3
Focus on refining the timing algorithm and sensor integration.
Assumption to check: Occasional bugs in lap timing accuracy.
Validate with people who use this workflow before building.
Hypothesis 4
Consider offering a free trial or lower entry price to attract more users.
Assumption to check: High price point for premium features.
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
Harry's LapTimer is the advanced tool for car enthusiast. It records all types of sensor data provided by your iPhone/iPod/iPad (or external sensors), combines them, and makes them available to optimize your drive. Over time, you will get insights on your car and in your driving, not known before. LapTimer offers more than 1300 predefined tracks world wide. With its assistants, it is extremely easy to setup - just click your track and drive. It fully automates your lap timing using GPS, and presents the results to all kinds of media. You are not limited to track driving only. For example, you may define your home and working locations as a 'track', collect statistics on different ways chosen, and analyze / optimize the time used every day. Want to show your drive to your friends? LapTimer Petrolhead and above generates beautiful in car video recordings with all kinds of data overlaid, ready to be presented - e.g. on youtube. Even without video, recorded data can be analyzed using purpose designed views, making it easy to analyze and improve your driving performance. Using online racing, you can use LapTimer in competition. LapTimer offers a Hall of Fame, allows watching you and your friends on track - all in real time. Compare your sector times, braking / acceleration points, and learn from each other. You can start with your plain iPhone in the beginning and add external GPS and OBD II sensors later, step by step, and as you need it. LapTimer itself comes in three different editions: LapTimer Rookie is the entry level with all you need for lap timing; LapTimer Petrolhead is the advanced version including lots of video features, and LapTimer Grand Prix is the edition for professionals including Multi Cam recording, Health Kit integration, and advanced sensor and analytics functionality. Please note that functionality depends on your device, the LapTimer edition chosen, and sometimes even external sensors added (like OBD II). Please visit our web page to get the full story. All edition can be upgraded later, all editions come with native iPhone and iPad support. There are quite expensive stand alone solutions for track days available. Be smart and own the leading edge tool simply by using your iPhone and LapTimer. Besides the professional area, there is no known solution that offers more functionality than LapTimer does - across the market. As our ambition is to offer the best tool, LapTimer is enhanced continuously. Please visit http://www.gps-laptimer.de for detailed information on versions, FAQs / documentation, in depth technology background information, online racing, and supported device configurations. Join our user community on http://www.gps-laptimer-forum.de to be involved in future development - all with first class support.
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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
@react-navigation/native
react-native-chart-kit
@react-native-async-storage/async-storage
expo-sensors
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.
