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. No subscription. No tracking. Your answers stay on your device.
Other system design prep tools charge per session, require internet, and ship your answers to OpenAI. SDA runs on your phone, costs nothing, and keeps your practice private.
| SDA | Hello Interview | Educative | ArchSim | |
|---|---|---|---|---|
| Price | Free | Subscription | $80+/yr | Subscription |
| Works offline | ✓ | — | — | — |
| Your answers stay on-device | ✓ | — | — | — |
| Native iOS & Android | ✓ | Web | Web | iOS only |
| 60-second arcade format | ✓ | — | — | — |
| No signup required | ✓ | — | — | — |
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), or Story Mode (capstone narratives).
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 9 PM reminder if you forget. 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.
Four 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.
Your answers stay on your device. Optional Apple/Google sign-in only to sync progress across devices.
Yes. No subscription, no ads, no paywalled levels today. 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. After install, all 50+ games + the daily challenge work without internet. Useful on planes, the subway, or any country with bad Wi-Fi.
They stay on your device. Cloud sync (optional, via Apple/Google sign-in) backs up your progress — game IDs, scores, streaks — but never the content of your answers.
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 60-second arcade gameplay. 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 (iOS 16+), iPad, and Android (10+). Optimized for both phone and tablet. Cloud sync keeps progress in sync if you switch.
It's in the lab. Tap "Notify me about AI Interview Practice" in Settings → About 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 under 60 seconds. Free to download. Works offline.