Your .env files are validated and out of Git by now, thanks to the last article on managing environment variables and secrets. The app boots with the right config in every environment. What it doesn't have yet is a shape that survives more than a handful of features.
This is part of the Full Stack SaaS Masterclass, a build-it-for-real series that takes a multi-tenant SaaS from an empty folder to production. Today's topic sounds boring compared to auth or payments, but I've seen more codebases rot from folder structure than from any single bad library choice.
Here's the thing about structure: nobody notices it on day one, when you have three routes and two services. Everybody notices it eighteen months in, when adding a field to an invoice means touching twelve files scattered across four unrelated folders. This article is about setting the shape early enough that it never becomes a rewrite.
Structure by feature, not by file type
The instinct most engineers start with is grouping by technical role: a controllers/ folder, a services/ folder, a dtos/ folder, a models/ folder. It looks tidy in a diagram. It falls apart the moment your app has more than about five features, because every change to one feature touches four different folders and you spend more time navigating than coding.
