> ## Documentation Index
> Fetch the complete documentation index at: https://system.muzemus.online/llms.txt
> Use this file to discover all available pages before exploring further.

# System overview

> How the frontend, backend, and database layers connect

MUZE is a three-tier web application with a clear separation between presentation, business logic, and data persistence.

## Request lifecycle

```mermaid theme={null}
sequenceDiagram
    participant Browser
    participant Firebase as Firebase Hosting
    participant Render as Render (NestJS)
    participant Neon as Neon PostgreSQL

    Browser->>Firebase: GET /orders
    Firebase->>Browser: index.html + JS bundle
    Browser->>Render: GET /api/v1/orders
    Note over Render: SessionGuard → PermissionsGuard → ScopeGuard
    Render->>Neon: SELECT ... WHERE "clientId" = $1
    Neon->>Render: rows
    Render->>Browser: 200 OK + JSON
```

## Three tiers

### Presentation (React SPA)

The frontend is a single-page application built with React, Vite, and Tailwind CSS, served as static files from Firebase Hosting. All page components are lazy-loaded, server state is managed by TanStack React Query, and forms use React Hook Form with Zod. See [Frontend architecture](/engineering/frontend-architecture).

### Business logic (NestJS API)

The backend is a NestJS application exposed as a REST API under the global prefix `/api/v1`. It runs on Render's Node 20 runtime on port 3001.

Key characteristics:

* Feature modules, each encapsulating one domain concern
* `ValidationPipe` with `whitelist: true` strips unexpected fields from all requests
* Global exception filters normalize all error responses
* Rate limiting via `@nestjs/throttler`: 100 requests per minute
* better-auth handler mounted on the Express instance at `/api/auth`
* Request timeout of 15 minutes for large report generation

See [Backend architecture](/system-architecture/backend-architecture).

### Data (Neon PostgreSQL)

The database is a serverless PostgreSQL instance on Neon, managed entirely through Prisma Migrate. Prisma Client is the only database access layer; there is no raw SQL in application code. `PrismaModule` is global, and better-auth stores sessions and users in the same database. See the [Data](/data/data-model-overview) tab.

## Deployment topology

The frontend and backend deploy independently. Firebase Hosting serves the SPA; Render runs the API; Neon holds the database; Cloudflare R2 stores uploaded files. The full topology and build commands are in [Deployment](/operations/deployment).

The frontend knows the backend URL through `VITE_API_BASE_URL`, baked into the build at compile time.