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
PepCal: Peptide Calculator
Pep Cal: Peptide Calculator is an ad-free tool exclusively for scientists, researchers and other enthusiasts
$2.99
PRICE
$2.99
No in-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.3
36 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 included15 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 PepCal: Peptide Calculator: map the core Utilities workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
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App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
Screenshots
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App Store description
Pep Cal: Peptide Calculator is an ad-free tool exclusively for scientists, researchers and other enthusiasts providing them with peptide reconstitution and mixing guidelines. The app is not meant for use by medical professionals. Peptide Calculator Features: 1) Reconstitution: Estimate approximately how much water is required for your peptides 2) Mixing Ratios: Explore possible mixing ratios for different sequences 3) Bacteriostatic Water: Use the bacteriostatic water calculations for your mi 4) Easy navigation: Intuitive user interface to navigate easily across the different features 5) Dark mode: Utilize dark mode to access the app at any time as per your convenience 6) Save your favorite calculations 7) Ads free: No ads to enhance your user experience 8) Put decimal numbers in for all values Disclaimer: Peptide Calculator is intended only for educational and laboratory purposes. It is not meant to be used by medical professionals and is not a medical guide or tool. Please consult with your local professional and follow your local regulations and guidelines.
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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 examples or tips for entering peptide sequences.
Assumption to check: Lack of user guidance for input sequences
Validate with people who use this workflow before building.
Hypothesis 2
Add features to edit or delete specific history entries.
Assumption to check: Limited history management
Validate with people who use this workflow before building.
Hypothesis 3
Enable users to export results via email or share to other apps.
Assumption to check: No export options for results
Validate with people who use this workflow before building.
Hypothesis 4
Optimize the app for better performance on low-end devices.
Assumption to check: Inconsistent performance on older devices
Validate with people who use this workflow before building.
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
React Navigation
React Native Paper
Expo Clipboard
BUILD KIT DIFFICULTY
Starter
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.
