Systems you can run
Press play and requests move through every part. Raise the traffic, slow a dependency down or switch a part off, then watch the design cope or fail.
About
Diagrams that run.
Simvora shows how software works by running it. Systems take real traffic, classes pass calls to each other, and algorithms step through their data, all live in your browser. You can pause any of it, break it, and look inside.
A diagram you can only look at hides the interesting part.
Boxes and arrows show where things are. They don't show what happens when traffic triples at 8 pm, when a cache goes cold, or when one slow dependency backs up everything behind it. That part usually gets imagined, a hundred times over.
Here you watch it once. The queue fills, the errors climb, and then the part that fixes it does its job, so you can see why it's there.
What's here
Three subjects, one way of learning them
Concept pages
One idea per page: 119 on system design, 73 on classes and patterns, 44 on data structures and algorithms. The hard ones run live.
Browse the conceptsSteps on three learning paths
Each path puts its pages and problems in order, and every step uses only what came before it.
See the pathsCode problems
Design the classes yourself in Java or TypeScript, and the checks point out what the design still gets wrong.
Find a problemBuild problem, and your own designs
Design a system against its requirements, trace each request through it, and let Review test it under load, spikes and failures. Build needs an account.
Open BuildHow a system gets here
Six steps before anything goes on the site
Research
It starts with how the real thing is built, from public engineering write-ups, papers, talks and documentation.
Requirements
What it has to do, and how well: the traffic, the latency, what may fail and what must not. With numbers from those sources.
Decisions
Every part is on the board because a requirement asks for it. There is no best design, only the best fit for the requirements.
Evolution
It starts small and grows. Each version breaks somewhere, and the next one adds the part that fixes it.
Failures
Then it gets broken on purpose: a dependency slows down, a cache goes cold, a spike arrives. Each one is a story you can run.
Checks
Each failure story says what should happen, and the simulator has to meet every one of those expectations before the system ships.
What you can count on
Free to use
Every page, simulation and path on the site is free.
No account needed to learn
Your progress stays in your browser. Sign in with Google or a passkey to keep it on every device, or to use Build.
Open source
The site's code is public on GitHub under the GNU AGPL 3.0.
Models, not benchmarks
The simulations show how a design behaves. They're for learning, not for sizing a real deployment.
Made by one developer, in the open.
Simvora is built by nexus-hash. More systems are on the way, and the learning paths already show where each one will go. Building products with AI agents comes next.
Found a mistake, or want a system covered? Write to support@simvora.dev.