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
CRUMB
CRUMB offers an easy to use and interactive introduction to electronic circuits
$7.99 · In-app purchases
PRICE
$7.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.4
140 ratings · Top 30%
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 included16 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 CRUMB: map the core Productivity 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
Focus on simplicity and essential features to avoid user fatigue.
Assumption to check: Users find task management tools overwhelming with too many features.
Validate with people who use this workflow before building.
Hypothesis 2
Implement robust sync with clear error handling and notifications.
Assumption to check: Sync issues between devices can lead to data loss.
Validate with people who use this workflow before building.
Hypothesis 3
Offer customizable themes and layouts to enhance user experience.
Assumption to check: Lack of customization options like themes or layouts.
Validate with people who use this workflow before building.
Hypothesis 4
Create a streamlined onboarding process with a tutorial to quickly introduce key features.
Assumption to check: Users feel the onboarding process is too long.
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
CRUMB offers an easy to use and interactive introduction to electronic circuits Fully realised in 3D, you can construct prototype circuits as you would at the workbench without the risk of terminal component failure or the hassle of ordering individual components CRUMB comes with a great selection of components to allow you to jump straight in to creating prototype circuits With the catalogue available, it is possible to study the workings of transistors & audio filtering, all the way to programming an EEPROM to run a basic program For the beginner, it is possible to learn and understand the basics of interactivity, and for the enthusiast it is possible to analyse and perfect prototypes before constructing real world models Using the built in oscilloscope and analysis views, it is possible to see clearly the interaction between components from within the wires themselves Through community feedback and suggestion, there will be many more components and features added. For a full feature list and development schedule please visit the website http://www.crumbsim.com
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
Zustand
Supabase
React Navigation
React Native Reanimated
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.
