Backend Overview

The backend lives in apps/backend/ and runs a Hono API server on Node.js. It uses Prisma for schema management, Kysely for typed queries, PostgreSQL for storage, and Redis (Valkey) for caching.

Folder structure

apps/backend/src/
  cache/         # Valkey (Redis) client and initialization
  config/        # Environment config, app constants
  db/            # Database client (Postgres + Kysely)
  features/      # Domain-organized business logic
  libs/          # Shared backend libraries and WebSocket setup
  middleware/     # Error handling, validation, auth, file uploads
  routes/        # HTTP route definitions (thin layer)
  sockets/       # WebSocket event definitions
  testing/       # Test utilities, mocks, setup
  utils/         # Shared helpers

Key patterns

• Features own business logic. Each domain (projects, notifications, auth) has its own folder in src/features/ with modules, database queries, mutations, and schemas. See How to organize features.

• Routes are thin. Route files validate input, read context, call a module function, and return a response. No business logic in routes.

• No try/catch. A centralized error middleware handles all errors. Throw typed errors (ApplicationError, AuthError, ValidationError) and let the middleware do its job.

• Validation goes through Zod. Every route that accepts input uses the validate() middleware with a Zod schema. This powers both runtime validation and the end-to-end type bridge to the frontend SDK.

Database access

• Prisma for schema definition, migrations, and seeding
• Kysely for typed SQL queries (reads and complex writes)
• Prisma for inserts, Kysely for everything else

Reads go in db/queries/, writes go in db/mutations/. See Prisma and Kysely.