About SysDesignPrep.com
SysDesignPrep.com is a place to practise the system design interview out loud: 83 real interview questions, each with a full reference answer and a walkthrough of a strong candidate answering it, an AI interviewer that sits you through the same question on a shared whiteboard, 188 study guides and 117 interactive concepts.
Why it exists
Onsite after onsite, the same round. I started interviewing again and kept making it to onsites. Every time, system design is where it fell apart. Rejection after rejection.
Prep stopped at the diagram. Most material ends at load balancer, cache, database, done. My high-level designs were fine. I got stuck when the interviewer asked how exactly I would handle a hot partition, or what happens when this queue backs up.
Two AI windows. So I practiced with AI: one chat interviewed me, and I asked my follow-up questions in a second chat so the interview stayed clean. But the second chat had no idea what we had discussed. I was re-explaining my design every time.
So I put it all in one room. It felt like pasting code into ChatGPT before the model moved inside the editor, where it could see everything. So I built myself a tool that keeps the interview, the whiteboard and the AI Mentor in one place. It turned into this site, and I still use it.
How the content is made
- Reference answers follow one written standard. Every question has functional and non-functional requirements with numbers, back-of-envelope estimates with the derivation shown, the components and the user flows through them with the API call at each step, and deep dives that weigh the alternatives, name the one chosen and answer the follow-up questions an interviewer asks next: 475 deep dives in all.
- Each question adds patterns the others do not. Questions are chosen for the building blocks they teach, not for company names, so the set covers caching, fan-out, real-time delivery, geospatial matching, money movement, contention for inventory, stream processing and workflow orchestration without repeating itself.
- Company attributions are reports, not endorsements. Which companies ask a question (62 of them) comes from public interview guides and candidate reports. It says where a question has been asked, nothing more.
- Interactive concepts are simulations, not animations. Each playground runs a deterministic model of the idea, and the numbers its page quotes come from running that model.
- The AI interviewer is given the reference answer as its private brief. It knows what a strong answer contains so it can probe what you leave out, but it is told never to read the answer out or steer you into repeating it, and to judge a different design that meets the requirements on its merits.
Corrections
Every question page has a way to report a problem. Or email support@sysdesignprep.com.