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System Design
Learn to architect scalable and reliable systems
Preparing this workspace.
System design mock interview
Pick a system or a company HLD or LLD round. The interviewer questions what you draw: scale, trade-offs and failure modes.
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Learn to architect scalable and reliable systems
Design classes and objects that survive changing requirements
System design mock interview
Design a real system out loud on a shared canvas while a voice AI interviewer watches what you draw. It pushes on requirements, back-of-envelope numbers, data models, bottlenecks and failure modes, and it questions the components you actually drew, not a summary you typed. Practise high-level and low-level design rounds whenever you want, without booking a person.
Step 1
A classic prompt (URL shortener, news feed, chat, rate limiter), one of 26 case studies, or a round scoped to a company.
Step 2
Ask about users, scale and the features that matter. The interviewer answers like a real one and expects you to drive.
Step 3
Sketch services, stores, queues and data flow on the canvas while you talk. The interviewer reads the diagram as you build it.
Step 4
Answer follow-ups on scale, consistency and what fails first, then read a scored report a minute after you finish.
System design rounds open a canvas the interviewer can see. When you add a cache, a queue or a second database, it asks why that component is there, what happens when it fails, and whether your numbers justify it. Feedback is about the design you drew, not a generic checklist.
Vague answers get follow-ups: how many requests per second, which consistency model, how the hot key is handled, what the read path looks like at 10x. You practise driving a 45-minute design discussion, which is the part most candidates never rehearse.
High-level design rounds cover distributed systems end to end. Low-level design rounds cover classes, interfaces, design patterns and concurrency, the object-oriented round many companies run alongside it. Coding rounds in the same product run your code in 6 languages, so one account covers the whole loop.
Scope a round to a company and role, and the interviewer uses that company's interview context and bar. 160 companies have interview data behind them, and resume-based rounds ask about the systems you have actually built.
A mock shows you where your design breaks. The learning paths are where you fix it, in the same account, with an AI interview one click from every topic.
12 families, 73 lessons and 26 worked case studies, from load balancing to global consistency.
12 families and 46 lessons on object-oriented design, SOLID, design patterns and concurrency.
The common system design interview questions in one list, each with an AI mock interview button.
Parking lot, elevator, rate limiter and the other LLD classics, ready to practise.
| Option | Price (USD) | What you get |
|---|---|---|
| Thita Starter | $0 | 2 AI interviews in your first week, then 1 a month. No card needed. |
| Thita Pro | $14.99/month or $75/year | 15 AI interviews a month (about $1 an interview), plus any 2 extra learning paths such as System Design and Low-Level Design, and both 90-day roadmaps. |
| Thita Elite | $29.99/month or $120/year | 30 AI interviews a month and all 11 learning paths, including System Design and Low-Level Design. |
| Hello Interview Premium | $95/year (sale price)[source] | System design courses and AI-guided practice. |
| interviewing.io human mock | From $179 per session[source] | One anonymous mock interview with a senior engineer. |
A year of Thita Pro costs less than one human system design mock and includes 15 AI interviews a month. Use AI rounds to get the reps in, and save a human session for a final check if you want one.
Forty-five minutes, one prompt, out loud on a whiteboard the interviewer reads. Then see where the design held up.