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
Caliber: Strength Training
Caliber is a science-based strength training app that combines resistance training, cardio, nutrition, and habit formation to help you build muscle, lose fat, and improve your overall fitness—for good.
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 4.8
5,798 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.
Build your own version
Build Kit
Make this idea yours
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 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 Caliber: Strength Training: 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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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 exercise database and include more workout templates.
Assumption to check: Limited workout variety compared to competitors
Validate with people who use this workflow before building.
Hypothesis 2
Implement thorough testing and user feedback loops to fix bugs.
Assumption to check: Some users report bugs with tracking features
Validate with people who use this workflow before building.
Hypothesis 3
Create a more user-friendly paywall with clear benefits.
Assumption to check: In-app purchase prompts can be intrusive
Validate with people who use this workflow before building.
Hypothesis 4
Integrate social challenges and community features to boost engagement.
Assumption to check: Lack of community features for social interaction
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
Caliber is a science-based strength training app that combines resistance training, cardio, nutrition, and habit formation to help you build muscle, lose fat, and improve your overall fitness—for good. TRAIN YOUR WAY • Free Version. Create and track unlimited workouts, access 600+ exercises, and train solo or with friends. • Caliber Plus. Maximize your results with coach-designed training plans, personalized progress tracking, nutrition targets and more. • Premium Coaching. Get 1-on-1 guidance from an elite-level personal trainer with a fully customized training and nutrition plan, in-app chat + video messaging with your coach and weekly progress reviews to keep you on track. CALIBER FEATURES (FREE VERSION) • Personalized Workouts. Create and track an unlimited number of workouts tailored to your goals. No gym required. • Detailed Exercise Tutorials. Learn proper form with step-by-step videos and pro tips from Caliber coaches. • Workout Groups. Train with friends or family in private groups. Your workouts and personal bests are shared with the group to keep you motivated. • Apple Health Integration. Sync your cardio, nutrition, and body stats from your wearable or connected device. UNLOCK MORE WITH CALIBER PLUS (OPTIONAL UPGRADE) • Coach-Designed Training Plans. Choose from 60+ structured plans tailored to your goals, experience level and schedule. • Strength Score. Measure how strong you are relative to your potential for your age and gender. • Strength Balance. Improve your posture and mobility by optimizing your training across key muscle groups. • Caliber Lessons. Gain expert insights on training and nutrition to accelerate your progress. • Advanced Training Features. Get personalized nutrition targets, create custom exercises and supersets, swap exercises, upload progress photos, and more. PREMIUM COACHING (OPTIONAL UPGRADE) • Work with an Elite-Level Coach. Train 1-on-1 with a dedicated coach to achieve your full potential in the gym and beyond. Caliber coaches are highly vetted, accredited personal trainers among the top 1% in their field. • Fully Personalized Plan. Your coach will design a training and nutrition program just for you based on your goals, experience and lifestyle. • Daily Motivation & Expert Guidance. Stay on track with in-app messaging, video form reviews, and individualized guidance. • Weekly Progress Reviews. Get in-depth analysis from your coach to optimize your training. • Fast Response Times. Your coach is available 24/7, typically replying within a few hours. • Guaranteed Results. On average, Caliber members improve their body composition by 20% or more within 12 weeks. If you don't see results, we'll refund the cost of the program. SEE WHAT OUR MEMBERS SAY • For detailed reviews from real Caliber members, visit our TrustPilot page at https://www.trustpilot.com/review/caliberstrong.com Terms of Use: https://caliberstrong.com/terms-of-service/ Privacy Policy: https://caliberstrong.com/privacy-policy/
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
Firebase
axios
react-navigation
react-native-chart-kit
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.
