The free, offline system design interview prep app. 50+ arcade-style games on caching, sharding, Kafka, Redis, and every other concept the interviewer is going to ask about. New: the AI Arcade, eight games on RAG, LLM serving, embeddings, guardrails, and GPU fleets. No subscription. No ads.
Other system design prep tools charge per session and need a connection. SDA is free, installs on your phone, and keeps working when the signal drops.
| SDA | Hello Interview | Educative | ArchSim | |
|---|---|---|---|---|
| Price | Free | Subscription | $80+/yr | Subscription |
| Works offline | ✓ | — | — | — |
| Native iOS & Android | ✓ | Web | Web | iOS only |
| Bite-sized arcade levels | ✓ | — | — | — |
| Start without signup | ✓ | — | — | — |
Competitor info as of May 2026. We're not affiliated with any of these tools; they're great in their own right. Different shape, different audience.
Designed so you can practice on the subway and still walk into an interview prepared.
Concept Arcade (building blocks), Problem Arcade (end-to-end designs), Tool Arcade (Redis / Kafka / Postgres), Story Mode (capstone narratives), or the new AI Arcade (RAG, LLM serving, ML systems).
Multiple-choice, ordering, API Builder, Architecture Builder, and Scenario-Why drills. Every level mixes formats so your brain actually engages.
One fresh challenge every day. Optional daily reminder at a time you choose. Build a streak that survives a full interview season.
A taste of the surface area. Dark arcade by default; playful sticker-card vibe available from Theme Lab.
Built for senior+ engineers prepping for FAANG and late-stage startups, but accessible enough for anyone curious about scale.
Eight games on the round that didn't exist three years ago: RAG, LLM serving, feed ranking, embeddings, feature stores, ML observability, AI guardrails, and GPU infrastructure.
Concept, Problem, Tool, and Story tracks covering the full system design interview surface area.
Chapter-by-chapter path from fundamentals to capstones. No guessing what to learn next.
One fresh challenge every day. Streak counter. Optional opt-in reminders.
End-to-end design narratives — walk the requirements, tradeoffs, and architecture like a real interview.
Train reasoning, not just recall. Every level asks you to justify the choice.
Drag components, draw connections, see if your design holds.
Walk-and-learn — every explanation reads to you over your AirPods.
Dark arcade or playful sticker — your eyes, your call.
No ads, no ad tracking, no data sold. Play Level 1 of any game as a guest; a free sign-in unlocks every level and syncs progress across devices.
Yes. No subscription, no ads, and no paid tiers — Level 2 and up just need a free account, not a payment. If we ever introduce paid features — most likely the upcoming AI Interview Practice — they'll be opt-in additions, never replacements for what's already in the app.
Yes. Once you're signed in, every game and the daily challenge work without internet; guests can play Level 1 of any game offline. Useful on planes, the subway, or any country with bad Wi-Fi.
They stay on your device unless you turn on the optional AI Coach, which sends the architecture you built for feedback. Cloud sync (via a free Google, GitHub, or email sign-in, plus Apple on iPhone and iPad) backs up your progress: game IDs, scores, streaks. Usage analytics are described in the privacy policy.
Those are great tools — they tend to be web-based, subscription-priced, and built around long-form video or AI-chat practice. SDA is a free mobile app built around short arcade levels. Use both if you want; we're optimized for the in-between moments (subway, lunch break) when you can't sit down for an hour of video.
iPhone, iPad, and Android. Optimized for both phone and tablet. Cloud sync keeps progress in sync if you switch.
A track of eight games on AI and ML system design: retrieval-augmented generation, LLM serving, feed ranking, embeddings, feature stores, ML observability, AI guardrails, and GPU infrastructure. Same arcade format, and it plays offline once you're signed in. It is live on the App Store now; the Android update is rolling out on Google Play. It is separate from AI Interview Practice below: the AI Arcade teaches you to design AI systems, while AI Interview Practice is an upcoming feature that grades your answers.
It's in the lab. Turn on "AI Interview Practice" under Future Features in Settings and we'll surface it the moment it's ready. It will run on-device (Apple Foundation Models on iOS 26+) so it stays free and offline.
Download System Design Arcade and start your first level in a minute. Free to download. Level 1 of every game plays offline, no account needed.