FormCheck - AI Workout Form Coach via Phone Camera

Real-time posture correction for gym-goers using phone camera + Claude Vision. Point your phone at yourself, get instant feedback on squat depth, deadlift alignment, shoulder position — no wearables, no trainers, just brutal honesty.

Difficulty

intermediate

What is it?

Gym form is where 80% of injuries and plateaus happen, but hiring a trainer costs $50-150 per session. Personal trainers use visual cues (knee alignment, spine angle, hip drive) to correct form in real time. FormCheck replicates this by using Claude Vision to analyze a live camera feed from a phone propped up in the gym. The user selects their exercise from a dropdown, presses record, performs 3-5 reps, and gets instant feedback on form breakdown points — 'your knees caved inward on rep 2', 'depth was good but bar path drifted forward'. The app stores form history and tracks improvement over weeks. Paid tier unlocks exercise-specific drill suggestions and video comparison (user's form vs form ideal). Why 100% buildable right now: Claude Vision API is stable and production-grade. Nexmo or Twilio WebRTC lets you stream phone camera to backend. Next.js handles the UI. Supabase stores workout history. Zero new model training needed — Claude's multimodal understanding is trained on fitness content. The hardest part is UX fluidity in gyms (poor wifi) which is solved via offline buffering and batch upload.

Why now?

Claude Vision launched stable API in late 2024 and pricing dropped to $0.003 per image by early 2026. Gym injuries and form anxiety peaked post-pandemic as casual gym-goers returned without coaching. Expo hot reload makes mobile iteration fast enough for solo dev.

▸Real-time video form analysis via Claude Vision
▸Exercise dropdown (squat, deadlift, bench, overhead press, rows) with biomechanics prompts
▸Form history + trend tracking (form breakdown points over 12 weeks)
▸Drill suggestions based on detected form issues
▸Offline video buffering for poor gym wifi, batch upload on connect

Target Audience

Gym enthusiasts aged 18-45 without personal trainers. ~2.5M gym members in US alone who skip leg day and wonder why their knees hurt. Target early: powerlifters and CrossFit athletes (10% of gym population, highly engaged, willing to pay).

Example Use Case

Jake, a 28-year-old software engineer, squats 3x per week but has lingering knee pain. FormCheck tells him his knees are caving on every rep due to weak quads. He uses the app for 6 weeks, follows the 'knee alignment' drill, and pain vanishes. He upgrades to paid after week 1 trial and stays for $120/year.

User Stories

▸As a powerlifter, I want to record my squat and get instant feedback on knee cave, so that I can fix form before it causes injury.
▸As a casual gym-goer, I want form history to show my progress over 8 weeks, so that I stay motivated and confident.
▸As a gym owner, I want to offer FormCheck
▸as a perk to members, so that I reduce liability and retention increases.

Acceptance Criteria

Form Analysis: done when Claude Vision returns JSON with detected form issues (e.g., {'issue': 'knees caved inward', 'severity': 'high', 'frame': 2}) within 5 seconds. Video Upload: done when user can record 10-second video and upload succeeds even on 4G. History: done when user can see all form checks from past 30 days with timestamps. Payment: done when Stripe checkout works and paid user sees unlimited checks immediately after upgrade.

Is it worth building?

$9.99/month × 100 users = $999 MRR by month 3. $9.99/month × 800 users = $7,992 MRR by month 8.

Unit Economics

CAC: $8 via Reddit + ProductHunt organic (assume 2% conversion from 500 impressions). LTV: $120 (12 months at $9.99/month with 60% retention). Payback: 1 month. Gross margin: 82% (after Claude API, hosting, payment processing).

Business Model

Freemium: 5 free form checks per week. Paid: $9.99/month unlimited checks + form history + drill suggestions.

Monetization Path

Free tier limited to 5 form checks/week to force upgrade. Upsell drill routines at $4.99/month. Enterprise tier for gyms at $199/month (unlimited users).

Revenue Timeline

First dollar: week 4 (beta upgrade). $1k MRR: month 5. $5k MRR: month 11. $10k MRR: month 18.

Estimated Monthly Cost

Claude Vision API: $60 (assuming 100 users, ~6 analyses/user/week), Vercel: $20, Supabase: $25, Firebase: $15, Stripe fees: ~$15. Total: ~$135/month at launch.

Profit Potential

Full-time viable at $5k–$12k MRR. Gym partnerships (revenue share) could accelerate to $50k MRR.

Scalability

High — can expand to all compound lifts, add team mode for gym partners, white-label for gym chains, AI personal training plan generator.

Success Metrics

Week 1: 200 signups. Week 2: 40 paid subscribers. Month 2: 85% form-check completion rate (shows engagement). Month 3: 60 avg reps analyzed per user per week.

Launch & Validation Plan

Survey 50 gym-goers on Instagram fitness accounts about form concerns. Build landing page. Get 10 beta testers from local CrossFit gym. Record their feedback for 2 weeks before writing code.

Customer Acquisition Strategy

First customer: Join local CrossFit gym, offer free 4-week trial to top 20 most engaged athletes in exchange for testimonials and referrals. Ongoing: Reddit r/fitness, r/gainit, r/Fitness, TikTok fitness creators, Instagram fitness hashtags, ProductHunt.

What's the competition?

Competition Level

Low

What's the roadmap?

Feature Roadmap

V1 (launch): Real-time form analysis for 8 exercises, history tracking, free tier. V2 (month 2-3): Exercise-specific drill suggestions, form trend graphs, email reminders. V3 (month 4+): Gym partnership program, team mode, white-label API for fitness apps.

Milestone Plan

Phase 1 (Week 1-2): Supabase setup, Expo camera integration, Claude Vision endpoint, basic UI. Done when form analysis works end-to-end on test video. Phase 2 (Week 3): Stripe integration, history storage, exercise dropdown, mobile polish. Done when 3 beta testers can sign up, pay, and record workouts. Phase 3 (Month 2): Analytics, email notifications, ProductHunt prep, customer support setup. Done when 50+ beta users active and churn under 10%.

How do you build it?

Tech Stack

Next.js, React Native (Expo for quick mobile), Claude Vision API, Supabase for form history storage, Firebase Realtime for frame buffering, Stripe for payments — build backend with Cursor, mobile UI with Lovable, camera component with v0.

Time to Ship

3 weeks

Required Skills

Claude Vision integration, React camera API, basic video streaming, form biomechanics knowledge not required (Claude knows it).

Resources

Anthropic Claude Vision docs, Expo camera library, React Native Camera docs, Supabase storage quickstart, YouTube fitness biomechanics videos for prompt tuning.

MVP Scope

1) Next.js landing page + auth (Supabase). 2) Expo app with camera feed + video upload. 3) Claude Vision integration endpoint to analyze single video frame per rep. 4) Form feedback display (text + emoji severity). 5) Basic history storage in Supabase. 6) Stripe subscription integration. 7) Exercise selector (8 exercises hardcoded). 8) Mobile UI with Lovable. 9) Frame extraction from video (one frame per rep). 10) Error tracking (Sentry). No team features, no community, no wearable sync.

Core User Journey

Sign up -> select exercise -> record video -> receive form feedback in 10 seconds -> see history -> upgrade to paid within 14 days.

Architecture Pattern

Phone camera feed -> Expo app -> local buffer (if offline) -> upload to Firebase Storage -> trigger Cloud Function -> Claude Vision API analyzes frame -> feedback stored in Supabase -> real-time response to mobile app via Supabase realtime.

Data Model

User has many WorkoutSessions. WorkoutSession has many FormChecks. FormCheck has one Exercise and one FormFeedback (text analysis). WorkoutSession stores metadata (date, exercise type, reps). FormFeedback stores Claude's response + severity score.

Integration Points

Claude Vision API for form analysis, Supabase for user data and form history, Firebase Storage for video buffering, Stripe for payments, Sentry for error tracking, Expo for mobile deployment.

V1 Scope Boundaries

V1 excludes: team features, live trainer marketplace, wearable integrations, AI-generated workout plans, social sharing, community forums, white-label gym apps.

Success Definition

A stranger finds FormCheck on ProductHunt, records a squat video, receives actionable form feedback within 30 seconds, upgrades to paid after trying free tier, and records workouts consistently for 8+ weeks.

Challenges

Claude Vision API cost at scale — each rep uses 2-3 API calls (~$0.05 cost). Requires smart batching and caching to stay under $40/month per user. Gym wifi is unreliable; must handle offline buffering gracefully without frustrating users.

Avoid These Pitfalls

Do not attempt real-time streaming analysis — buffer frames and analyze offline. Do not store raw video permanently; delete after analysis to reduce costs and liability. Do not target raw beginners; start with experienced lifters who value precision over hand-holding (easier to upsell, faster to convert).

Security Requirements

Auth: Supabase Auth with email + Google OAuth. RLS on all user tables: users can only see their own form_checks. Rate limiting: 20 form analyses per hour per user (prevent API abuse). Input validation: video file size max 50MB, video duration max 60 seconds. Data retention: delete video frames after 24 hours, retain feedback text for 12 months. GDPR: offer data export and deletion endpoints.

Infrastructure Plan

Hosting: Vercel for Next.js backend. Database: Supabase (Postgres) for user data and feedback. Storage: Firebase Storage for temporary video buffering (auto-delete after 24h). CI/CD: GitHub Actions on push to main. Environments: dev (localhost), staging (Vercel preview), prod (Vercel main). Monitoring: Sentry for errors, Vercel Analytics for traffic. Expo app deployed via Expo Application Services (EAS). Cost breakdown: Vercel $20, Supabase $25, Firebase $10, Stripe processing ~$15. Total: ~$70/month baseline.

Performance Targets

Expected launch load: 50 DAU, 200 req/day. API response target: under 500ms for Claude Vision analysis. Video upload target: under 5 seconds on 4G. Page load: under 2 seconds (Vercel edge). Caching: Claude response cached for 1 hour per exercise (same form issues repeat). Session storage via Supabase.

Go-Live Checklist

☐Security audit: RLS rules tested, video deletion confirmed
☐Payment flow: test Stripe checkout with 5 different cards
☐Error tracking: Sentry dashboard live and receiving errors
☐Monitoring: Vercel Analytics configured, CloudWatch alerts set
☐Custom domain: formcheck.fitness DNS configured with SSL
☐Privacy policy and terms: published, mention no medical claims
☐Beta sign-off: 5 beta users confirm form feedback is accurate
☐Rollback plan: document how to revert Vercel deployment
☐Launch post: ProductHunt post drafted, Reddit r/fitness post ready, Twitter thread outlined.

How to build it, step by step

1. npx create-expo-app formcheck && cd formcheck. 2. npm install expo-camera supabase stripe-react-native. 3. Set up Supabase project, create users and form_checks tables with RLS. 4. Build camera screen in Expo with video recording (Lovable can generate UI). 5. Create Next.js backend route for Claude Vision: POST /api/analyze-form (receives video frame). 6. Integrate Claude Vision API in backend route, store response in Supabase. 7. Add Stripe subscription logic to Next.js. 8. Test full flow locally (record video, upload, receive feedback). 9. Deploy backend to Vercel, mobile app to Expo. 10. Set up Sentry error tracking, launch to ProductHunt.

Generated

March 22, 2026

Model

claude-haiku-4-5-20251001

← Back to All Ideas