Highloady

LeetCode for system design. Build distributed architectures on a canvas, throw real traffic at them, and find out what breaks — before production does.

Get started Browse challenges →no signup · runs in-browser

01 — LIVE PREVIEW

BriefSimulation

~/survive-the-launch-spike

CHALLENGE · BEGINNER

Survive the Launch Spike

A product launch sends 10× your normal traffic. Keep latency and errors inside budget while thousands of new users pour in.

WIN CONDITIONS

Sustain 5,000 users

p99 latency < 200ms

Error rate < 1%

highloady@sim — 14 nodes · 4,200 users

edge-cdn

28%

gateway

44%

app-server

61%

postgres

73%

simulating✓ all systems nominalp99 142ms · 0.0% err

02 — HOW IT WORKS

Read the challenge

Win conditions, fail conditions, and a time limit. Know what “passing” means before you draw a box.

Build your architecture

Drag from 17 component types onto the canvas and wire them into a system that can take the load.

Watch it run

Simulate real traffic, watch nodes heat up, and tune until every goal turns green.

03 — WHAT'S INSIDE

Component types

Servers, caches, queues, gateways, brokers — the real building blocks.

Live

Real-time simulation

Traffic flows, nodes heat up, metrics tick second by second.

40+

Structured challenges

From your first cache to multi-region failover, graded by difficulty.

∞

Random events

Spikes, failovers and thundering herds hit when you least expect it.

Start with a beginner challenge.

~/challenges/survive-the-launch-spike — 8 min

Get started