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
Tube Exits by Station Master
Co-created by Geoff Marshall, a two-times Guinness World Record Holder for travelling to all Tube stations in the fastest time possible (a record he held most recently from 2013–2015)
$5.99 · In-app purchases
PRICE
$5.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 1.0
1 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 included14 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 Tube Exits by Station Master: map the core Travel 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
Enhance features with user-generated content and reviews.
Assumption to check: Limited functionality and user engagement.
Validate with people who use this workflow before building.
Hypothesis 2
Implement a live-update feature using user contributions.
Assumption to check: Inaccurate or outdated information.
Validate with people who use this workflow before building.
Hypothesis 3
Focus on a clean, user-friendly interface with better navigation.
Assumption to check: Difficult navigation and poor UX design.
Validate with people who use this workflow before building.
Hypothesis 4
Offer a free trial or freemium model to attract more users.
Assumption to check: High price point without clear value.
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
Co-created by Geoff Marshall, a two-times Guinness World Record Holder for travelling to all Tube stations in the fastest time possible (a record he held most recently from 2013–2015). http://www.tubeworldrecord.co.uk/ Tube Exits (previously Exit the Tube) contains details of the best door position to be nearest the exit at every station on the London Underground, original 84 Overground (pre-June 2015) stations and Docklands Light Railway. It also shows you the interchange corridors, passageways and lifts. The only exits App with correct door positions for new S-Stock trains and the new Tottenham Court Road Northern Line station. The information in Tube Exits is built-in so it is available at all times underground, without an internet connection. Note: Tube Exits is not a route planning App. London's Transport Network is constantly changing and evolving rapidly and we continually update the information in Tube Exits to reflect changes to the network and from community contributions and corrections. Please send any corrections and contributions via the Contact section of the App.
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
Axios
React Navigation
React Native Maps
BUILD KIT DIFFICULTY
Intermediate
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.
