# How to Vibe Code Your Own Strong (and Stop Paying for It)

> Think less. Lift more.

- Site: https://strong.app
- Category: Fitness & Workout Tracker
- Platforms: iOS app, Android app, Apple Watch app
- Verdict: **Solid side project** (65/100 vibecodeable)
- Estimated effort: 3-4 weeks part-time

## Verdict

Build a personal offline-first mobile workout tracker with Expo and SQLite, but the Apple Watch companion and flawless local sync will test your persistence.

At $4.99/mo or $30/yr, paying for Strong is entirely rational if you just want to lift weights without friction. However, vibecoding a personal React Native clone using Expo SQLite is a deeply satisfying project. The core engineering hurdle is not the CRUD UI, but ensuring that SQLite writes never lag mid-set and that your background sync queue handles cellular dropouts in concrete gym basements without corrupting local state. If you drop the Apple Watch app and focus purely on the phone experience, you can build a functional personal replacement over a few weekends.

### What you can't replicate

- 15 years of accumulated user trust and App Store authority
- Frictionless companion app watchOS architecture optimized over a decade
- Community-driven exercise database refinement

## What it does

Digital workout tracker and gym log designed for weightlifting and strength training, with routine planning, set logging, rest timers, and historical progress analytics.

### Core features

- Offline-first local workout logging (SQLite)
- Custom routine builder with supersets and warm-up calculators
- Active workout session runner with rest timers and previous set indicators
- Exercise library with custom exercise creation and muscle group categorization
- Historical progress charts (1RM, volume, max weight)
- Cross-device cloud synchronization queue
- Apple Health / Google Fit data syncing
- Data export (CSV)

## The business

### Pricing

- Free Tier: Free — Limited active routines (3 custom routines) and basic historical views.
- Strong PRO Monthly: $4.99/mo — Unlimited routines, advanced analytics, and cloud backups.
- Strong PRO Annual: $29.99/yr — Billed annually for heavy users.
- Strong PRO Lifetime: $99.99 — One-time purchase for permanent access.

Founded 2011.
Team size: 1-10.

## The hard parts

- Building a bulletproof offline-first sync queue that survives zero-reception gym environments without data loss or sync conflicts
- Achieving instant sub-second touch interaction during an active workout session when fatigued
- Designing a performant local database schema that calculates rolling 1RM and volume trends across tens of thousands of sets without UI stutter
- Apple Watch companion app real-time state synchronization over Bluetooth BLE under strict battery constraints

## How to vibe code Strong

### Prerequisites

- Node.js (free): Required to run Expo and React Native tooling.
- Expo CLI / EAS (free): For compiling and testing the mobile app on iOS and Android devices.
- GitHub (free): Version control and repository hosting.

### Recommended AI tools

- Cursor: Ideal for iterative mobile UI design, Tailwind/NativeWind styling, and component refactoring.
- Claude Code: Excellent for scaffolding local SQLite models, complex migration logic, and background sync state machines.

### Stack

- Frontend: React Native with Expo (TypeScript)
- Backend: Node.js with Express / REST API for cloud backups
- Database: Expo SQLite (local offline-first) + PostgreSQL on Railway (cloud backup)
- Auth: better-auth
- Payments: None (personal use clone)
- Other: NativeWind for styling, Expo Haptics for active workout feedback, Victory Native or similar for charts

### Hosting

- Railway (Hosting the optional backup REST API and PostgreSQL cloud sync sink): $5/mo

### Build guide

1. **Expo Project Scaffolding & Offline SQLite Setup** — Initialize a TypeScript Expo project with file-based routing and configure Expo SQLite for local-first storage.

```
Create a new Expo React Native project using TypeScript and expo-router. Install expo-sqlite and set up a local database initialization layer. Create tables for exercises, routines, routine_exercises, workouts, workout_sets, and personal_records with proper foreign key constraints and indexes. Write a migration utility that runs on app boot to ensure local schema consistency. Implement a repository pattern in TypeScript to handle CRUD operations for exercises and workouts entirely offline. Ensure all queries execute synchronously or asynchronously without blocking the UI thread.
```

2. **Exercise Library & Custom Exercise Management** — Build the exercise catalog screen supporting muscle group filtering, equipment types, and custom exercise creation.

```
Build an Exercise Library screen in React Native with a search bar and category filters (Muscle Group: Chest, Back, Legs, Shoulders, Arms, Core; Equipment: Barbell, Dumbbell, Machine, Bodyweight). Implement a modal sheet allowing users to create custom exercises with custom muscle targets. Store these locally in the SQLite exercises table. Ensure selecting an exercise navigates smoothly back to the active routine builder with zero latency.
```

3. **Routine Planner Screen** — Create the routine management interface allowing users to group exercises, set default warm-ups, and organize workout templates.

```
Implement the Routine Planner interface. Users can create named routines, add multiple exercises from the library, reorder them, and configure default target sets, reps, and weights. Add support for grouping exercises into supersets. Save routine templates to SQLite. Ensure the UI feels snappy and responsive, using FlatList virtualization and NativeWind for clean dark-mode styling.
```

4. **Active Workout Session Runner & Rest Timer** — Build the core workout logging screen with active set completion, previous performance hints, and an automatic rest timer.

```
Build the Active Workout session runner screen. When a routine starts, insert a new workout record and render each exercise with its logged sets. For each set, display the weight and reps from the previous workout session as a light grey hint badge. Allow users to tap 'Done' to log a set, triggering subtle haptic feedback via expo-haptics. Upon completing a set, automatically start a customizable countdown rest timer (e.g., 90 seconds) with a persistent floating banner and audio/vibration alert when time expires. All changes must instantly commit to the local SQLite database.
```

5. **Progress Analytics & History Views** — Implement historical workout logs, personal record detection, and progress visualization charts.

```
Build the History tab displaying past completed workouts grouped by date, showing total volume, duration, and exercise summaries. Implement a Progress/Analytics tab where users can select any exercise and view historical 1RM estimates (calculated via Epley formula: weight * (1 + reps/30)) and max weight lifted over time rendered using Victory Native charts. Ensure aggregation queries run efficiently against local SQLite indexes.
```

6. **Cloud Sync Queue & Backup** — Set up a background synchronization queue to back up local workout modifications to a remote PostgreSQL database when online.

```
Implement a lightweight Node.js/Express backend deployed on Railway with PostgreSQL and better-auth. In the Expo app, build a sync queue service that tracks local database mutations with a sync_status flag ('synced', 'pending'). When network connectivity is restored (using NetInfo), batch upload pending workout logs and routines to the server, handling basic conflict resolution by latest timestamp. Provide a manual 'Export CSV' utility in settings that compiles all local SQLite data into a formatted CSV file and triggers the native share sheet.
```

### Cost vs paying

**Starting costs (one-time):**

- Apple Developer Account (optional for sideloading/testflight): $99/yr
- Total: ~$119 one-time

**Ongoing costs (monthly):**

- Railway PostgreSQL & Backend Hosting: $5/mo
- Total: ~$5/mo

- Paying for the SaaS instead: $4.99/mo
- Build time: 25-35 hours
- AI tool credits: $20 (Cursor/Claude Pro)
- Break-even: 24 months (or instant if building for learning)

## Sources

- [Strong Official Website](https://strong.app)
- [Apple App Store - Strong Workout Tracker Gym Log](https://apps.apple.com/us/app/strong-workout-tracker-gym-log/id464254577)
- [Google Play Store - Strong Workout Tracker Gym Log](https://play.google.com/store/apps/details?id=io.strongapp.strong)
- [Tracxn - Strong Fitness PTE. LTD. Company Profile](https://tracxn.com)