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Computer science, made visible

The conceptscollege skips.In 60 seconds.

buildwith.rex turns the engineering ideas interviewers love — scaling, system design, payments, caching — into short animated reels you'll actually remember. One new concept every week.

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Frame from the reel: Bigger server, or more servers? 1:00
Vertical vs horizontal scaling

Bigger server, or more servers?

Results day, the portal freezes. One person says get a bigger server, another says add four more. Both are right, in the right place, and picking the wrong one quietly burns money.

Vertical scalingHorizontal scalingLoad balancersCloud cost

Comment SCALE on the reel to get the free kit in your DMs.

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Frame from the reel: What is system design? 0:48
Scaling, load balancers, caches, databases

What is system design?

Ten users and everything works. A million users at once and the server falls over. That moment is where system design begins, explained with a roadside tea stall.

ServersLoad balancersCachingDatabases

Comment DESIGN on the reel to get the free kit in your DMs.

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How it works

One concept. One picture. One minute.

Every reel takes a single idea and draws it — servers, packets, queues — so you see how it behaves instead of memorising a definition.

Start from a moment you know

A results portal freezing. A payment stuck on Pending. The idea arrives through something you've lived.

Watch the system move

Hand-built motion graphics show the parts and how they talk to each other, synced to the narration.

Keep the interview answer

Each reel ends on the exact sentence you can say in an interview. Comment the keyword for a free deep-dive kit.

New every week

Learn the concepts interviews actually ask.

Free, no courses, no paywall. Just the idea, clearly.

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