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
Gravl: AI Personal Trainer
Gravl is an AI personal trainer for strength training
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 4.9
6,193 ratings · Top 5%
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 should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
What's included18 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 Gravl: AI Personal Trainer: map the core Health & Fitness 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
Gravl is an AI personal trainer for strength training. It builds your plan, coaches you through every set, and tells you exactly how much weight to lift next time. AUTOMATIC PROGRESSIVE OVERLOAD Gravl estimates your one-rep max from your logged history and prescribes the next session from it. Reps climb set by set; when the ladder fills, the weight steps up, snapped to the plates or stack you actually have. Rate a set Easy or Hard and the next prescription adjusts. TRAIN ON YOUR WRIST, WITHOUT YOUR PHONE A standalone Apple Watch app. Log sets and reps, run rest timers, and finish a whole session from the watch. Syncs with Apple Health, Garmin and Strava. STRENGTH SCORE See how your lifts compare against standards for your body weight and sex, tracked over time across every muscle group. BUILT AROUND YOUR GYM, NOT A GENERIC TEMPLATE Gravl accounts for the equipment you own, which muscles are still recovering, what you trained last session, and which lifts you've neglected. 300+ trainer-led exercise videos, downloadable for offline use. Free to start. Full training plans, the Apple Watch app and analytics on Gravl Premium. Privacy: https://gravl.ai/privacy Terms: https://gravl.ai/terms Terms (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/
Written user reviews are not shown here. Check current App Store reviews >
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 AI-driven dynamic adjustments based on user performance.
Assumption to check: Limited personalization options for workout plans.
Validate with people who use this workflow before building.
Hypothesis 2
Add social sharing and challenge features.
Assumption to check: No social features for sharing progress.
Validate with people who use this workflow before building.
Hypothesis 3
Provide clearer visualizations and summaries of user progress.
Assumption to check: Inconsistent tracking of progress metrics.
Validate with people who use this workflow before building.
Hypothesis 4
Simplify subscription tiers and provide clear value propositions.
Assumption to check: Complex subscription management.
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
Supabase
Zustand
react-native-reanimated
expo-notifications
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.
