Anatomy of an App

When you ask an AI to "add a login page" or "save this to the database," it's quietly making decisions about a half-dozen moving parts. If you don't know those parts exist, the answers read like a foreign language — and you can't tell a good one from a confused one.

This chapter is a map. It won't make you an engineer, but it will let you point at any piece of a modern app and say what it does and where it lives. Once you have the map, every other chapter stops being abstract: you'll know which box a problem lives in before you start describing it. We'll keep it plain — no jargon without a definition, and one running example (a user clicking a button) traced through every layer.