Simulation Library

Ten real systems to design and break. Pick one and start building.

Design Twitter Timeline

Build a feed that scales to millions of fan-outs without melting your write path.

CachingFan-outFeed generationRedisKafka

45 minIntermediate

Start

Scale PostgreSQL

Take a single-node database from first index to a sharded, replicated cluster.

IndexesReplicationPartitioningQuery optimization

50 minAdvanced

Start

Database Query Planner

A visual EXPLAIN ANALYZE simulator for reading query plans like an expert.

EXPLAIN ANALYZEQuery plansCost estimationIndexes

30 minIntermediate

Start

Distributed Cache Simulator

Tune eviction policies and TTLs while watching hit ratio move in real time.

RedisCache hit ratioTTLEviction policies

35 minBeginner

Start

Load Balancer Playground

Compare routing algorithms under bursty, uneven traffic in real time.

Round RobinLeast ConnectionsWeightedSticky Sessions

25 minBeginner

Start

API Gateway Simulator

Wire up auth, rate limits, routing and caching in front of live traffic.

AuthenticationRate limitingRoutingCaching

40 minIntermediate

Start

Microservice Failure Lab

Kill services on purpose and design retries, circuit breakers and fallbacks.

Kill servicesRetryCircuit breakerFallbackTimeout

55 minAdvanced

Start

Message Queue Explorer

Kafka vs RabbitMQ — ordering guarantees, consumer groups and DLQs, side by side.

Kafka vs RabbitMQOrderingConsumer groupsPartitionsDead letter queues

45 minAdvanced

Start

System Design Interview

An AI interviewer, a live whiteboard, and real-time feedback on your tradeoffs.

AI interviewerArchitecture whiteboardLive feedback

60 minExpert

Start

Cloud Cost Simulator

Scale from 100 to 10M users and watch your infrastructure bill react.

100 users1,000 users100,000 users10M users

30 minIntermediate

Start