Every app you've ever used is two things: the movie the audience watches, and the production machinery nobody sees.
The front end is the finished film — everything the user sees and touches. It splits into UI (the interface: layout, buttons, colors) and UX (the experience: how you move through it). Instagram's feed, likes, explore page and profile are all front end.
The back end is the production system behind the film: where data is stored, logic runs, and requests get processed. Instagram's storage of your photos, its login checks, its APIs — all back end. The reason this split matters to a non-programmer is that every vibe-coding decision you'll make lands on one side or the other, and the platforms price and fail differently on each side.
The session's running example: Instagram. What you scroll is the movie; the databases, authentication and APIs underneath are the crew, sets and editing suite that made it.
This is the vocabulary every later concept hangs on — auth, APIs, databases, hosting are all 'which part of the production is this?' questions. Get the split and vibe-coding stops feeling like magic.
The app IS what I see on screen.
What you see is roughly half. Storage, logic, identity and processing live in a back end you never see — and it's where most vibe-coding failures happen.
Front end is the movie that is shown to you... Back end is the production system behind the movie.0:17:43
The KB itself splits the same way: the rendered pages are front end, build_site.py plus the YAML corpus is the back end. That the site is static — no server logic at all — is exactly why it's cheap and unbreakable.
Go deeper
In one line: Front end is what the user sees and experiences (UI + UX — the finished movie); back end is where logic, storage, processing, and coordination happen (the production system behind it).
Instagram example: feed, likes, explore, profile = front end; storage, auth, APIs = back end (0:21:46)
UI = interface/layout, UX = experience/navigation; both combine into front end
Open any app you use daily and narrate the split out loud: name three front-end things you can see and three back-end things that must exist for them to work.
▶ Watch this taught: 0:15:42
Answer from memory first — the recall attempt is what makes it stick. Then reveal.
What's the difference between UI and UX?
UI is the interface — layout, buttons, visual design. UX is the experience — how you navigate and how it feels. Together they make up the front end.
Instagram's like button, its photo storage, its login check: which side is each on?
Like button: front end. Photo storage and login check: back end.















