Walk through one. Then sit one.

A recorded system design interview between an interviewer and a strong candidate, played one turn at a time. You press Next, the candidate answers, and the whiteboard fills in as they talk: requirements, numbers, the API, then a design that gets fixed one bottleneck at a time, then the deep dives. At the key decisions it pauses and asks what you would say before showing what the candidate said.

A chat beside the interview, never part of it. Ask it anything about what you have seen so far (why this database, what a term means, whether your own idea would work) and it answers with the interview and the whiteboard in front of it. Each turn also comes with suggested questions whose answers are written in advance; those are free for everyone. Live questions are part of Pro.

You are the candidate. An AI interviewer runs the round the way a real one does: it states the problem, asks one thing at a time, probes what you said and what you drew on the whiteboard, and ends with a debrief (a score out of 100, what was strong, what was missing, and a note on each stage with a link to the same stage of the walkthrough).

Your choice at the start. Timed is interview conditions: a 45-minute clock the interviewer owns, and the coach is off. With the coach there is no clock and the coach sits beside you; it gives hints rather than answers unless you ask it outright, and the debrief says the round was coached.

The Design a URL Shortener walkthrough, with no account, including the pauses and the suggested questions. Sign in and you can pick one more walkthrough free. On a mock interview, anyone can hear the interviewer open the round. Everything else is Pro: every other walkthrough, live questions to the coach, and answering the interviewer.

Reading gives you the final answer. A walkthrough shows you how a strong candidate gets there out loud (the order, the pacing, the numbers, and the design being fixed one problem at a time) and lets you stop and ask why. The mock then makes you produce it yourself, under pressure, with someone following up on the weak part.

Every walkthrough, including every one added later; live questions to the coach, including comparing your answers with the candidate’s; AI mock interviews, timed or with the coach; and the company-style mock interviews. All three plans include the same thing; they differ only in how you pay.

Monthly and annual plans renew until you cancel. Cancel from the billing portal at any time and you keep access until the end of the period you paid for. Lifetime is a single payment with no renewal.

Yes. Open the billing portal from the pricing page and switch plans; Stripe prorates the unused part of the current period.

Yes, on a first purchase. Email us within 7 days of it, having gone through fewer than 3 Pro walkthroughs and started fewer than 3 mock interviews, and it is refunded in full. Renewals are not refundable, so cancel before the renewal date if you are done. The Terms have the details.

Not for the free walkthrough, and not to hear the AI interviewer open a round. Signing in with Google unlocks a second walkthrough of your choice, and is needed to buy Pro.

Public interview guides and candidate reports. They indicate where a question has been reported, not a verified dataset, and a company name never implies endorsement.

Senior and staff loops at large tech companies, where the interview is 45 to 60 minutes, expects numbers, and spends most of its time on deep dives. Mid-level candidates use it too; the walkthroughs explain every term as they go, and the coach will explain anything they do not.