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
Combine Fluids
Combine Fluids
$0.99 · In-app purchases
PRICE
$0.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 3.7
3 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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Combine features and design from your favorite apps.
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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/
Preview a sample Build Kit No email needed
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 Combine Fluids: 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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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
Expand fluid database and allow user submissions for new fluids.
Assumption to check: Limited fluid selection options compared to competitors.
Validate with people who use this workflow before building.
Hypothesis 2
Optimize app performance for various device specifications.
Assumption to check: Inconsistent performance on older devices.
Validate with people who use this workflow before building.
Hypothesis 3
Implement onboarding tutorials and tooltips for first-time users.
Assumption to check: Lack of user guidance on how to use the app.
Validate with people who use this workflow before building.
Hypothesis 4
Add social sharing features for results on social media.
Assumption to check: No sharing options for fluid mix results.
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
Combine Fluids The creators of the top-rated app, Oilfield Calendar, offer a solution to another oilfield problem. Combine Fluids is designed to provide fast answers for everyday calculations. Combine Fluids, a simple to use calculator for the oil and gas professional. • Combine up to 10 different fluid types. • Save different mix possibilities for different wells. • From Mud Men to Derrick Men, anyone combining fluids will have a new favorite app. • Built by Oilfield guys for Oilfield user’s, putting out the best productivity apps in the industry. How to use Combine Fluids • Select weather you have volume limitations or not. • Enter your current or desired mud density, the mixing requirements will then be displayed for that information. • Save your parameters and create more volume combinations as needed. You’ve got your hardhat, steal toes, and safety glasses, now add Combine Fluids to the essential tools you need when working in the patch. Make your calculations easy, keep your life turning to the right. ** Feel free to drop us a line! We’re always listening to your suggestions and strive to improve our apps! If you have any feedback just contact us, [email protected] ** ** Are you happy with the Combine Fluids app? We’d love to hear about it! Please take a moment to leave us a nice review, it truly helps us continue creating great tools for the industry! ** While you’re in the sharing mood, go ahead and post about it on Facebook too, Be Good!
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
TypeScript
React Navigation
React Native Clipboard
React Native Share
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.
