The Amazon System Design Interview: SDE II and SDE III

Amazon publishes prep pages for both levels. The SDE II page and the SDE III page describe these loops:

Coaching guides add two details from candidate reports. At SDE II, the design round is often run by the hiring manager for the team you would join. And the interviewer usually picks a problem from their own team’s work, so the prompt may sound like a real Amazon system more than a textbook one.

Amazon’s pages say 55 minutes per interview. Candidate guides describe the design round as about an hour with roughly 30 minutes to walk through the design itself. The rest goes to the Leadership Principles: one coaching guide says the behavioral part often takes more than half of every interview, design rounds included.

Plan for that. At SDE II, thirty minutes fits requirements, a quick sizing, a working design and one deep dive. At SDE III, the guides describe about 10 minutes for requirements and a high-level sketch, then most of the slot on two or three components. Either way, agree the requirements fast, get a design that works on the board, and spend your depth where the interviewer is looking.

Amazon’s SDE II page names the objectives for the design question: practicality, accuracy, efficiency, reliability, optimization and scalability. Amazon does not say how they are weighed, but practicality is the one coaching guides on SDE III repeat: they list practical designs you could build over over-engineered ones.

The same guides list what the round scores at each level. At SDE II: how you think about the architecture, scale and trade-offs, how well you pin down the requirements, and how clear you and your diagram are. SDE III adds failure modes, data consistency, the cost of running what you built, and customer obsession.

Each Amazon interviewer is given competencies to cover, some technical and some based on the Leadership Principles. So your design interviewer may ask a behavioral question too. Have a story ready about a system you designed, a trade-off you made and what it cost. Our Leadership Principles guide covers how to build those stories.

After the loop, the interviewers write their feedback and vote, and a Bar Raiser, an interviewer from outside the team, runs the debrief. Candidates report votes of inclined or not inclined, and ratings per area. One self-described Bar Raiser on Blind said it is very common to raise the bar on the principles and miss on the technical parts. A strong story does not rescue a weak design.

Amazon describes the Bar Raiser’s job as keeping the debrief about data. For your design round, that means the notes need specific moments: a requirement you set with a number, a part you chose because of it, a failure you raised before anyone asked.

For how the whole loop fits together, read our Amazon loop guide.

Hello Interview’s Amazon guides list these among the most asked, from candidate reports:

Notice how many are shaped like Amazon’s own business: lockers, parcels, streaming, notifications. The SDE II list leans toward a complete system with one hard part. The SDE III list leans toward contention and consistency: two buyers on one seat, two editors on one line, messages that must arrive in order. What each one needs, and the deep dives interviewers push toward, is in 62 system design interview questions, and who asks them.

Amazon lets you choose. Its virtual interview page suggests a diagramming tool on your computer with the window shared, a free web whiteboard such as Miro, or paper held up to the camera, over Zoom or Amazon Chime (read October 24, 2026). The SDE II page also links to guidance on Bluescape.

Pick one tool, practise in it until boxes and arrows take seconds, and test the screen share before the day. If you go with paper, use a thick pen and write large: the interviewer has to read it through a webcam.

The same prompt can come up at both levels. What changes is who drives and how deep you go. Here is how coaching guides and level write-ups described the difference when we read them on October 24, 2026:

A mid-level candidate can take a hint and lose little. At SDE III, the hint is itself the signal: if the interviewer has to raise scale or failure, that usually ends up in the feedback.

Candidates and coaching guides describe the design round as the one that often decides between SDE II and SDE III. Coaching guides also report more senior candidates getting mid-level offers at the big companies, and name two causes. The first is over-engineering: queues, caches and search clusters for a problem one database would carry. Every extra part is something to defend, and practicality is on Amazon’s own list. The second is waiting to be led. At SDE III, every time the interviewer has to ask "what about scale?" or "what if this fails?", it counts against you.

An Amazon commenter in a Blind thread on senior design rounds summed up the difference in three things: comparing more than one approach, recommending one from experience, and raising metrics, alarms, observability, security and upkeep without a prompt. Those are what an SDE III design sounds like. Practise saying them before you are asked.

Hello Interview’s case against over-engineering is simple. Every extra part is another place for a mistake, more to run, and more to fail, and interviewers notice a tool that is named and never explained. If you name a technology, be ready to say in one sentence what it does in your design.

With half the hour on the design, every minute has a job. Spend about five on requirements: three things the system must do, a few targets with numbers, and one thing you leave out and why. Spend two or three on the numbers that matter, and say which component each one picks. Then about twelve on a design with a path for every requirement, walking one request from end to end. Keep the last ten for the deep dive the interviewer cares about, and for what you would monitor.

At SDE III, compress the first part. Get requirements, numbers and a design that works on the board in about ten minutes, then spend the rest on two or three components, each down to its keys, its locks and what happens when it fails. Say why you chose those components: that choice is part of what the interviewer writes down.

Start simple. A service and one database that meet the requirements beat a diagram full of parts you cannot defend, and practicality is on Amazon’s own list. Add a queue or a cache only when you can name the problem it solves, ideally with a number you already wrote down.

Before the day, ask your recruiter which tool you will use and practise in it. Prepare two stories about systems you built: what you chose, what you gave up, and what you would change. They serve the Leadership Principles part of the slot, and they give you real experience to draw on when the interviewer asks why you made a choice.

Star Interview runs a practice system design interview on a shared whiteboard. Choose Amazon and your level, and your AI interviewer picks a question for that level, drawing on the questions Amazon candidates report where it can, then answers with numbers, runs the deep dives and asks what breaks first. Your report shows the level your design read as, so you can tell an SDE II round from an SDE III one before Amazon does.