Learn by playing,
not just reading.
An interactive playground for technical concepts. Every page is a live simulation you can poke, twist, and break — built for engineers who learn with their hands.
Featured track
Start with something foundational
Rate limiting — the first track wired end-to-end with live prototypes you can break.
Rate Limiting
Control request throughput so a noisy client cannot starve everyone else. Compare the five canonical algorithms side-by-side.
Cache Write Policies
Three ways to handle a write when you have a cache in front of the store. Each policy is a different bet about durability, throughput, and how stale your data is allowed to get.
Cache Eviction
When the cache fills up, something has to go — and which one you pick decides your hit rate. Ten classic policies, side-by-side.
Garbage Collection
How a runtime reclaims memory you stopped using — without you ever calling free(). Eight algorithms, from the counter on every object to the collectors that run alongside your program.
Memory Allocation
Before garbage collection ever runs, something has to hand out the memory. Six allocators — four ways to pick a hole, plus the two structured schemes real kernels actually ship.
How it works
Three steps. No syllabus.
Open the platform mid-coffee, leave with a sharper mental model. The whole loop is built to fit a lunch break.
Pick a topic
Browse a curated set of CS and system-design topics. Each is broken into bite-sized concepts.
Explore a concept
Read the why, then keep going. Diagrams, code, and short notes that earn their place.
Play with the prototype
Twist the inputs, break it, watch the system react. Then check yourself with a quick quiz.
Why visual learning
The fastest path from confused to fluent.
Working memory loves motion
Static diagrams leave gaps that take days of reading to fill. Watching a system run closes them in minutes.
Small inputs, big intuition
Sliding a single dial reveals the trade-off space far faster than enumerating it in prose.
You can't fake understanding here
If the simulation breaks when you stress it the way the algorithm should break, you actually get it.
Ready to stop reading about systems and start running them?
The scaffold is here. Real prototypes and explanations are landing topic-by-topic — start where you're curious.
Open the topic library