FitForge — Forge your best self

AI-powered fitness app: personalized workout plans (home or gym), AI diet plans, a live workout tracker, meal/water/weight tracking, progress charts and an AI coach chat.

Stack: Next.js 16 (App Router) · Tailwind CSS v4 · Supabase (Auth, Postgres + RLS, Storage) · Claude API (Sonnet 5.5 for plans & coach, Haiku 4.5 for quick estimates) · Recharts

Setup

1. Install

npm install

2. Create a Supabase project

1. Create a free project at supabase.com.
2. Apply the database migrations in supabase/migrations/, either:
   • CLI: npx supabase login, npx supabase link --project-ref <ref> (asks for the database password), then npx supabase db push; or
   • SQL Editor: paste and run each file in order — 0001_init.sql, 0002_progress_photos.sql, 0003_full_persistence.sql.
3. Authentication → URL Configuration: set Site URL to http://localhost:3000 and add http://localhost:3000/auth/callback to Redirect URLs.
4. (Optional, faster local testing) Authentication → Providers → Email: turn off "Confirm email".
5. (Optional) Authentication → Providers → Google: enable it to use "Continue with Google".

3. Environment variables

cp .env.local.example .env.local

Fill in your Supabase URL, anon key and service-role key (Project Settings → API), and your Anthropic API key (console.anthropic.com).

4. Seed the exercise library (~870 exercises with images)

npm run seed:exercises

Source: free-exercise-db (public domain).

5. Run

npm run dev

Open http://localhost:3000.

Scripts

Command	What it does
npm run dev	Dev server
npm run build	Production build
npm test	Unit tests (health calculations)
npm run typecheck	TypeScript check
npm run lint	ESLint
npm run seed:exercises	Load the exercise library into Supabase

How it fits together

• Health math is deterministic (lib/fitness/calculations.ts): BMI, Mifflin–St Jeor BMR, TDEE, calorie target, macros, water. The AI receives these numbers — it never invents them.
• Workout plans (lib/ai/plans.ts): the exercise library is filtered by the user's location, equipment and level; Claude may only pick exercise ids from that list, and output is validated with Zod.
• AI coach (app/api/ai/chat/route.ts, lib/ai/coach.ts): streams replies, knows the user's profile/plan/logs, and can propose plan changes, meal swaps or meal logs that the user applies with one tap.
• Security: every user table has Row Level Security; API keys stay server-side; daily AI quotas per user (consume_ai_quota SQL function).

Deploy

Push to GitHub and import into Vercel. Add the same env vars (set NEXT_PUBLIC_SITE_URL to your production URL) and add https://your-domain/auth/callback to Supabase Redirect URLs.

FitForge provides general fitness guidance, not medical advice.