Welcome to Kosuke Template
Kosuke Template is a production-ready, multi-tenant SaaS starter built with modern web technologies. Get your SaaS application up and running in minutes, not months.
🚀 Tech Stack
- Next.js 15 (App Router) + React 19 + TypeScript
- FastAPI (Python) - Microservice backend on Fly.io for extensible business logic
- Clerk - Authentication with Organizations, teams, and roles
- PostgreSQL (Neon) + Drizzle ORM - Type-safe database with auto migrations
- Stripe - Subscription billing and payments
- Resend + React Email - Transactional emails with React components
- Vercel Blob - File storage with CDN
- Sentry - Error tracking and performance monitoring
- Tailwind CSS + Shadcn UI - Beautiful, accessible components
- Vitest - Fast testing with React Testing Library
🎯 Who Is This For?
- Solo founders who want to launch quickly
- Development teams building multi-tenant applications
- Agencies needing a robust starter for client projects
- Engineers who want to learn modern SaaS architecture
Services Reference
Quick reference for all integrated services:
| Service | Purpose | Free Tier | Dashboard |
|---|---|---|---|
| Clerk | Authentication & Orgs | 10k MAUs | dashboard.clerk.com |
| Stripe | Billing & Subscriptions | Test mode | dashboard.stripe.com |
| Neon | PostgreSQL Database | 3 GB | console.neon.tech |
| Vercel | Application Hosting | Unlimited | vercel.com |
| Fly.io | Microservice Hosting | 3 VMs | fly.io/dashboard |
| Resend | Email Delivery | 3k emails/mo | resend.com |
| Sentry | Error Monitoring | 5k events/mo | sentry.io |
When to Upgrade
- Clerk: > 10,000 monthly active users
- Stripe: Ready for real payments (switch to live mode)
- Neon: > 3 GB storage or need dedicated compute
- Vercel: > 100 GB bandwidth or need team features
- Fly.io: Need more than 3 VMs or dedicated compute
- Resend: > 3,000 emails/month
- Sentry: Exceeding error or performance event limits
Features
Organizations & Teams
Complete multi-tenancy with Clerk Organizations:
- Create unlimited organizations with team invitations
- Admin and member roles with customizable permissions
- Automatic webhook sync to your database
- Organization-scoped data isolation
- Organization-level billing and subscriptions
Subscription Management
Stripe billing integration with automated sync:
- Three tiers: Free, Pro ($20/mo), Business ($200/mo)
- Real-time webhook updates + 6-hour cron backup sync
- Hosted checkout pages with automatic receipts
- Feature gating based on subscription tier
- Test mode for testing without real charges
Email System
Transactional emails with React Email and Resend:
- Build email templates with React components
- Welcome emails sent automatically on signup
- Preview templates locally with development server
- High deliverability optimized for transactional mail
- Custom domain verification for production
File Uploads
Vercel Blob storage for user content:
- Profile images and organization logos
- Automatic image optimization and CDN delivery
- 5 MB size limit with format validation (JPEG, PNG, WebP)
- Admin-only access control for organization logos
- Base64 upload via tRPC for seamless integration
Microservice Architecture
Python FastAPI engine service on Fly.io:
- Auto-scaling microservice (scales to zero when idle)
- FastAPI with Pydantic validation and auto-generated docs
- Sentry integration for error tracking and monitoring
- UV for fast dependency management
- Health checks and observability built-in
- Extend with custom business logic as needed
Error Monitoring
Sentry integration for production confidence:
- Automatic error tracking (client, server, API, microservices)
- Performance monitoring with transaction tracking
- Session replay for debugging (10% sample, 100% on errors)
- Source maps for readable TypeScript stack traces
- Release tracking with automatic deployment tagging
🚦 Quick Start
Want to use Kosuke Template for your SaaS?
→ Follow the Deployment Guide to deploy in 60-90 minutes.
Want to contribute to Kosuke Template?
→ See the Contributing Guide in the README for local development setup.
🤝 Community & Support
- Documentation: You're reading it! Explore the sidebar for detailed guides.
- GitHub: github.com/filopedraz/kosuke-template
- Issues: Report bugs or request features on GitHub
📄 License
Kosuke Template is open source and available under the MIT License.