app-shell

• SKILL.mdcore · 13,048 bytes

# The App Shell

The shell is the part of the screen that does not change when the user navigates: the bar across the top, whatever sits in it, and in heavy tools a strip along the bottom. Everything between them belongs to the application. The shell is small, and it carries more weight than its size suggests — it is the only thing a user sees on every screen of every tool.

## The Shell Belongs to the Estate, Not to the App

One company rarely has one application. It has a public site, a shop, a customer portal, an internal admin tool, and something older that nobody wants to touch but that people depend on. The user crosses between them during a working day, and each crossing is where the sense of one company either holds or breaks.

**The rule: the top bar is estate-level furniture. The app owns everything below it.** An app that restyles the shared bar to fit its own look has taken something that was not its to change — the bar's job is to be the one fixed point.

But *fixed* is not the same as *full*. What the shell contains may shrink to whatever of its jobs are still unanswered here; what remains is identical — same position, same behaviour, same wording. Quantity flexes, treatment does not.

This also settles a hierarchy question that otherwise gets argued per team. Anything *above* the application in scope lives in the shell; anything *within* the application lives in the app's own navigation.

| Lives in the shell (above the app) | Lives in the app's own nav (within it) |