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+# Backend API
+
+> FastAPI-based REST API with async SQLAlchemy, JWT authentication, and comprehensive testing.
+
+## Overview
+
+Production-ready FastAPI backend featuring:
+
+- **Authentication**: JWT with refresh tokens, session management, device tracking
+- **Database**: Async PostgreSQL with SQLAlchemy 2.0, Alembic migrations
+- **Security**: Rate limiting, CORS, CSP headers, password hashing (bcrypt)
+- **Multi-tenancy**: Organization-based access control with roles (Owner/Admin/Member)
+- **Testing**: 97%+ coverage with security-focused test suite
+- **Performance**: Async throughout, connection pooling, optimized queries
+
+## Quick Start
+
+### Prerequisites
+
+- Python 3.11+
+- PostgreSQL 14+ (or SQLite for development)
+- pip and virtualenv
+
+### Installation
+
+```bash
+# Create virtual environment
+python -m venv .venv
+source .venv/bin/activate  # On Windows: .venv\Scripts\activate
+
+# Install dependencies
+pip install -r requirements.txt
+
+# Copy environment template
+cp .env.example .env
+# Edit .env with your configuration
+```
+
+### Database Setup
+
+```bash
+# Run migrations
+python migrate.py apply
+
+# Or use Alembic directly
+alembic upgrade head
+```
+
+### Run Development Server
+
+```bash
+uvicorn app.main:app --reload --host 0.0.0.0 --port 8000
+```
+
+API will be available at:
+- **API**: http://localhost:8000
+- **Swagger Docs**: http://localhost:8000/docs
+- **ReDoc**: http://localhost:8000/redoc
+
+## Development
+
+### Project Structure
+
+```
+app/
+├── api/              # API routes and dependencies
+│   ├── routes/       # Endpoint implementations
+│   └── dependencies/ # Auth, permissions, etc.
+├── core/             # Core functionality
+│   ├── config.py     # Settings management
+│   ├── database.py   # Database engine setup
+│   ├── auth.py       # JWT token handling
+│   └── exceptions.py # Custom exceptions
+├── crud/             # Database operations
+├── models/           # SQLAlchemy ORM models
+├── schemas/          # Pydantic request/response schemas
+├── services/         # Business logic layer
+└── utils/            # Utility functions
+```
+
+See [docs/ARCHITECTURE.md](docs/ARCHITECTURE.md) for detailed architecture documentation.
+
+### Configuration
+
+Environment variables (`.env`):
+
+```bash
+# Database
+POSTGRES_USER=postgres
+POSTGRES_PASSWORD=your_password
+POSTGRES_HOST=localhost
+POSTGRES_PORT=5432
+POSTGRES_DB=app_db
+
+# Security (IMPORTANT: Change these!)
+SECRET_KEY=your-secret-key-min-32-chars-change-in-production
+ENVIRONMENT=development  # development | production
+
+# Optional
+BACKEND_CORS_ORIGINS=["http://localhost:3000"]
+CSP_MODE=relaxed  # strict | relaxed | disabled
+
+# First superuser (auto-created on startup)
+FIRST_SUPERUSER_EMAIL=admin@example.com
+FIRST_SUPERUSER_PASSWORD=SecurePass123!
+```
+
+⚠️ **Security Note**: Never commit `.env` files. Use strong, unique values in production.
+
+### Database Migrations
+
+We use Alembic for database migrations with a helper script:
+
+```bash
+# Generate migration from model changes
+python migrate.py generate "add user preferences"
+
+# Apply migrations
+python migrate.py apply
+
+# Generate and apply in one step
+python migrate.py auto "add user preferences"
+
+# Check current version
+python migrate.py current
+
+# List all migrations
+python migrate.py list
+```
+
+Manual Alembic usage:
+
+```bash
+# Generate migration
+alembic revision --autogenerate -m "description"
+
+# Apply migrations
+alembic upgrade head
+
+# Rollback one migration
+alembic downgrade -1
+```
+
+### Testing
+
+```bash
+# Run all tests
+IS_TEST=True pytest
+
+# Run with coverage
+IS_TEST=True pytest --cov=app --cov-report=term-missing -n 0
+
+# Run specific test file
+IS_TEST=True pytest tests/api/test_auth.py -v
+
+# Run single test
+IS_TEST=True pytest tests/api/test_auth.py::TestLogin::test_login_success -v
+
+# Generate HTML coverage report
+IS_TEST=True pytest --cov=app --cov-report=html -n 0
+open htmlcov/index.html
+```
+
+**Test Environment**: Uses SQLite in-memory database. Tests run in parallel via pytest-xdist.
+
+### Code Quality
+
+```bash
+# Type checking
+mypy app
+
+# Linting
+ruff check app
+
+# Format code
+black app
+isort app
+```
+
+## API Documentation
+
+Once the server is running, interactive API documentation is available:
+
+- **Swagger UI**: http://localhost:8000/docs
+  - Try out endpoints directly
+  - See request/response schemas
+  - View authentication requirements
+
+- **ReDoc**: http://localhost:8000/redoc
+  - Alternative documentation interface
+  - Better for reading/printing
+
+- **OpenAPI JSON**: http://localhost:8000/api/v1/openapi.json
+  - Raw OpenAPI 3.0 specification
+  - Use for client generation
+
+## Authentication
+
+### Token-Based Authentication
+
+The API uses JWT tokens for authentication:
+
+1. **Login**: `POST /api/v1/auth/login`
+   - Returns access token (15 min expiry) and refresh token (7 day expiry)
+   - Session tracked with device information
+
+2. **Refresh**: `POST /api/v1/auth/refresh`
+   - Exchange refresh token for new access token
+   - Validates session is still active
+
+3. **Logout**: `POST /api/v1/auth/logout`
+   - Invalidates current session
+   - Use `logout-all` to invalidate all user sessions
+
+### Using Protected Endpoints
+
+Include access token in Authorization header:
+
+```bash
+curl -H "Authorization: Bearer <access_token>" \
+  http://localhost:8000/api/v1/users/me
+```
+
+### Roles & Permissions
+
+- **Superuser**: Full system access (user/org management)
+- **Organization Roles**:
+  - `Owner`: Full control of organization
+  - `Admin`: Can manage members (except owners)
+  - `Member`: Read-only access
+
+## Common Tasks
+
+### Create a Superuser
+
+Superusers are created automatically on startup using `FIRST_SUPERUSER_EMAIL` and `FIRST_SUPERUSER_PASSWORD` from `.env`.
+
+To create additional superusers, update a user via SQL or admin API.
+
+### Add a New API Endpoint
+
+See [docs/FEATURE_EXAMPLE.md](docs/FEATURE_EXAMPLE.md) for step-by-step guide.
+
+Quick overview:
+1. Create Pydantic schemas in `app/schemas/`
+2. Create CRUD operations in `app/crud/`
+3. Create route in `app/api/routes/`
+4. Register router in `app/api/main.py`
+5. Write tests in `tests/api/`
+
+### Database Health Check
+
+```bash
+# Check database connection
+python migrate.py check
+
+# Health endpoint
+curl http://localhost:8000/health
+```
+
+## Docker Support
+
+```bash
+# Development with hot reload
+docker-compose -f docker-compose.dev.yml up
+
+# Production
+docker-compose up -d
+
+# Rebuild after changes
+docker-compose build backend
+```
+
+## Troubleshooting
+
+### Common Issues
+
+**Module Import Errors**
+```bash
+# Ensure you're in the backend directory
+cd backend
+
+# Activate virtual environment
+source .venv/bin/activate
+```
+
+**Database Connection Failed**
+```bash
+# Check PostgreSQL is running
+sudo systemctl status postgresql
+
+# Verify credentials in .env
+cat .env | grep POSTGRES
+```
+
+**Migration Conflicts**
+```bash
+# Check migration history
+python migrate.py list
+
+# Downgrade and retry
+alembic downgrade -1
+alembic upgrade head
+```
+
+**Tests Failing**
+```bash
+# Run with verbose output
+IS_TEST=True pytest -vv
+
+# Run single test to isolate issue
+IS_TEST=True pytest tests/api/test_auth.py::TestLogin::test_login_success -vv
+```
+
+### Getting Help
+
+See our detailed documentation:
+
+- [ARCHITECTURE.md](docs/ARCHITECTURE.md) - System design and patterns
+- [CODING_STANDARDS.md](docs/CODING_STANDARDS.md) - Code quality guidelines
+- [COMMON_PITFALLS.md](docs/COMMON_PITFALLS.md) - Mistakes to avoid
+- [FEATURE_EXAMPLE.md](docs/FEATURE_EXAMPLE.md) - Adding new features
+
+## Performance
+
+### Database Connection Pooling
+
+Configured in `app/core/config.py`:
+- Pool size: 20 connections
+- Max overflow: 50 connections
+- Pool timeout: 30 seconds
+- Connection recycling: 1 hour
+
+### Async Operations
+
+- All I/O operations use async/await
+- CPU-intensive operations (bcrypt) run in thread pool
+- No blocking calls in request handlers
+
+### Query Optimization
+
+- N+1 query prevention via eager loading
+- Bulk operations for admin actions
+- Indexed foreign keys and common lookups
+
+## Security
+
+### Built-in Security Features
+
+- **Password Security**: bcrypt hashing, strength validation, common password blocking
+- **Token Security**: HMAC-SHA256 signed, short-lived access tokens, algorithm validation
+- **Session Management**: Database-backed, device tracking, revocation support
+- **Rate Limiting**: Per-endpoint limits on auth/sensitive operations
+- **CORS**: Explicit origins, methods, and headers only
+- **Security Headers**: CSP, HSTS, X-Frame-Options, etc.
+- **Input Validation**: Pydantic schemas, SQL injection prevention (ORM)
+
+### Security Best Practices
+
+1. **Never commit secrets**: Use `.env` files (git-ignored)
+2. **Strong SECRET_KEY**: Min 32 chars, cryptographically random
+3. **HTTPS in production**: Required for token security
+4. **Regular updates**: Keep dependencies current
+5. **Audit logs**: Monitor authentication events
+
+## Monitoring
+
+### Health Check
+
+```bash
+curl http://localhost:8000/health
+```
+
+Returns:
+- API version
+- Environment
+- Database connectivity
+- Timestamp
+
+### Logging
+
+Logs are written to stdout with structured format:
+
+```python
+# Configure log level
+logging.basicConfig(level=logging.INFO)
+
+# In production, use JSON logs for log aggregation
+```
+
+## Additional Resources
+
+- **FastAPI Documentation**: https://fastapi.tiangolo.com
+- **SQLAlchemy 2.0**: https://docs.sqlalchemy.org/en/20/
+- **Pydantic**: https://docs.pydantic.dev/
+- **Alembic**: https://alembic.sqlalchemy.org/
+
+---
+
+**Note**: For project-wide information (license, contributing guidelines, deployment), see the [root README](../README.md).