NestJS

House conventions for NestJS backends on v11 / Express 5. Apply them to code you are writing or changing — don't restructure untouched modules unless asked.

Examples throughout use an invented shipment domain purely to make the shape concrete. Read the structure, not the names.

Layering

Two layers, and the dependency arrow points one way only.

core/   domain + infrastructure. No controllers, no HTTP.        → core only
app/    features. Controllers, DTOs, guards, middleware, CQRS.   → app + core

A core module that needs to reach into a feature is telling you the concept it owns sits in the wrong layer — move the concept down rather than importing upward. Keeping the arrow honest is what lets a core module be driven by an HTTP request, a cron job, a CLI, or a queue consumer without dragging a controller along.

Always apply