I used to think my systems were unbreakable. Then one broke in production.

For a long time I designed systems the way most of us do: draw boxes, connect arrows, add a load balancer, add a cache, add a replica. On the whiteboard, it looked bulletproof.

Then a real spike hit. One slow database query held its connection a little too long. The pool filled up, requests queued behind it, timeouts piled on, and the whole service went down in minutes. Nothing was wrong with any single box. The design couldn't take the load I had never actually tested.

That incident taught me that system design isn't about drawing the right diagram. It's about answering harder questions:

→ How much traffic can this actually handle?
→ What breaks first, and why?
→ What happens when a cache is flushed, a database dies, or a whole zone goes down?

You can't answer those by staring at a diagram, and most of us can't afford to load-test real infrastructure just to learn.

So I built the tool I wished I'd had: ServerSloth, a free system design simulator that runs in your browser.

• Build with 212+ real components: EC2, EKS, Aurora, Redis, Kafka, Lambda and more
• Send up to millions of simulated users through your design
• Break things on purpose: kill nodes, add latency, flush caches, fail a zone
• See exactly what failed, with the real error message and the numbers behind it

No sign-up needed. It's free for everyone.

👉 serversloth.ferrixlabs.in

I'd love for you to try it, break something, and tell me what you think in the comments. Honest reviews, missing components, confusing bits, feature ideas: all of it helps.