Systa — Distributed systems, made visible.

Don't memorize system design — run it. Watch caches miss, queues back up and shards rebalance, then fix them yourself. Free to start on iPhone and Android.

Download on the App Store · Get it on Google Play

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Playground: design it, stress it, fix it

Drop in servers, caches and queues, push traffic through your design and watch where it buckles. Find the bottleneck before production does.

Real case studies: how big apps actually scale

46 case studies — from Design a URL Shortener and Design a News Feed to Design a Chat System — walked through section by section with the trade-offs explained.

Every concept, as a simulation

33 live simulations: load balancers, rate limiters, circuit breakers, caches, replication, sharding, consistent hashing, message queues, consensus, DNS, CDNs, TLS and AI systems like RAG and transformer attention.

13 courses, 103 lessons

• Foundations of Distributed Systems
• Scaling & Load Balancing
• APIs & Communication
• Protocols & Wire Formats
• Data Storage & Replication
• Caching & CDNs
• Messaging & Queues
• Consistency & Consensus
• Architecture & Operations
• Cloud & Operations
• Reliability & Resilience
• Security
• AI & LLM Systems

Frequently asked questions

What is Systa?

Systa is a mobile app for learning system design by doing. Instead of memorizing diagrams, you run interactive simulations of load balancers, caches, queues, replication, sharding, consensus and more, then learn the pattern behind each one in short lessons and real case studies. It is available for iPhone and Android.

Is Systa free?

Yes, Systa is free to start. The free tier includes the first 5 lessons, the Load Balancer and Cache simulations, two case studies (URL Shortener and News Feed) and the design playground. Systa Pro unlocks all 103 lessons, all 33 simulations, all 46 case studies, quizzes, flashcards and interview prep.

Is Systa good for system design interview prep?

Yes. Systa includes 88 system design interview prompts, each with a 30-second answer, a full answer, key points to hit, trade-offs, follow-up questions and red flags. Case studies such as Design a URL Shortener, Design a News Feed and Design a Chat System walk through requirements, capacity estimates and architecture the way interviewers expect.

What system design topics does Systa cover?

Systa has 13 courses: Foundations of Distributed Systems, Scaling & Load Balancing, APIs & Communication, Protocols & Wire Formats, Data Storage & Replication, Caching & CDNs, Messaging & Queues, Consistency & Consensus, Architecture & Operations, Cloud & Operations, Reliability & Resilience, Security, and AI & LLM Systems.

Which simulations are included?

Systa has 33 interactive simulations, including Load Balancer, Rate Limiter, API Gateway, Autoscaling, Circuit Breaker, Cache, Cache Stampede, Replication, Sharding, Consistent Hashing, LSM-Tree, B-Tree, Bloom Filter, Message Queue, Saga vs 2PC, Consensus (Raft), DNS Resolution, CDN, TLS Handshake, Tokenization, Transformer Attention and a RAG Pipeline.

Does Systa work offline?

Yes. All lessons, simulations and case studies are bundled in the app, so Systa works fully offline with no account or sign-up required.

Which devices does Systa support?

Systa runs on iPhone (iOS 17 or later) and Android phones (Android 10 or later).