Stack & Architecture

FastSaaS is a production-ready SaaS template built with FastAPI (backend) and React (frontend). It provides a complete foundation for building multi-tenant SaaS applications with subscription billing,

Tools

Backend:

• FastAPI - High-performance Python web framework

• SQLAlchemy - ORM with Pydantic for validation

• PostgreSQL - Production database

• Alembic - Database migrations

• JWT - Token-based authentication

Frontend:

• React with TypeScript - Type-safe UI development

• Vite - Fast build tool

• Tailwind CSS - Utility-first styling

• React Router - Client-side routing

Infrastructure:

• Docker & Docker Compose - Containerized development

• Stripe - Payment processing and subscription management

• Resend - Transactional emails (optional)

• Sentry - Error tracking and monitoring (optional)

Architecture Overview

Backend Architecture

The backend follows a feature-based modular architecture:

app/
├── main.py              # FastAPI application entry point
├── settings.py          # Environment configuration
├── db.py               # Database connection and session management
├── initial_data.py     # Database seeding
├── api/               # API endpoints organized by domain
│   ├── auth/          # Authentication endpoints
│   ├── tenants/       # Multi-tenant management
│   ├── payments/      # Stripe integration
│   ├── items/         # Example CRUD resource
│   └── super_admin/   # Super admin features
├── adapters/          # External service integrations
│   ├── email/         # Email providers (Resend, Fake)
│   └── payment/       # Payment providers (Stripe, Fake)
├── models/            # SQLAlchemy database models
├── utils/            # Authentication and authorization utilities
└── tests/            # Test suite

Frontend Architecture

The frontend uses feature-based organization:

frontend/src/
├── features/          # Feature modules
│   ├── authentication/
│   ├── subscription/
│   ├── tenants/
│   ├── members/
│   ├── items/
│   ├── settings/
│   └── admin/
├── shared/           # Shared components and contexts
├── types/            # TypeScript type definitions
└── utils/            # Utility functions

Design Patterns

Multi-tenancy:

• Each user can belong to multiple tenants

• Data is scoped by tenant UUID

• Role-based access control (Admin, Member)

Authentication:

• JWT-based authentication with access and refresh tokens

• Access tokens expire in 30 minutes

• Refresh tokens expire in 30 days

• Support for email/password and Google OAuth

External Data:

• Invoices are fetched directly from Stripe API (not stored locally)

• Subscriptions and payment methods are synced via webhooks

Dependency Injection:

• FastAPI dependencies for authentication (get_current_user)

• Tenant context extraction (get_current_tenant)

• Admin checks (require_admin, require_super_admin)