How to Practice for a System Design Interview (and Get a Mock With a Senior Engineer)
This guide is for software engineers, mid-level to staff, with a system design round coming up. It covers a practice plan, how to get a senior engineer to run a mock with you, a 60-minute agenda for that session, and a rubric they can fill in.
To practice for a system design interview, run timed 45-minute rounds out loud: clarify requirements, estimate scale, sketch the design, go deep on one component and defend trade-offs. For a mock interview with a senior engineer, pick someone who has recently interviewed at your target level, send the job description first, and ask them to interrupt and score you.
What a system design interview is really testing
A system design interview is an open-ended conversation about building something large, such as a messaging service or a news feed. There's no single right answer, and the interviewer usually isn't waiting for a particular diagram. They're watching how you get to one.
In practice, that comes down to a few questions. Do you pin down what the system has to do before you draw boxes? Do rough numbers on the load shape your choices? Do you go deep on the hardest part instead of staying shallow everywhere? Can you say what each choice gave up? And can the interviewer follow your thinking without pulling it out of you?
That last one catches strong engineers off guard. Plenty of people who design well at work go quiet in the room, or solve it in their heads and only narrate the result. The round grades reasoning you say out loud, so practice out loud too.
What changes by level
The same prompt is graded differently by level. Roughly:
- Mid-level: a design that works end to end, sensible basics for storage and caching, and clear answers when you're pushed.
- Senior: you drive the conversation, size the system yourself, and raise failure cases before the interviewer does.
- Staff: you stay calm with a vague prompt, talk about how the design would evolve or be migrated, and weigh what it costs other teams.
Confirm your level and round with your recruiter before you start, since it changes what a good answer looks like.
How to practice system design interviews: a 4-stage plan
Most system design interview practice fails in one of two ways: reading with no reps, or reps with nobody saying what's missing. Work through these stages in order, and loop back when a mock exposes a gap.
- Refresh the building blocks you need to explain trade-offs.
- Work classic prompts yourself before you read a worked design.
- Run solo timed rounds out loud, and grade the recording.
- Move to live mocks with someone who interrupts and pushes back.
1. Refresh the building blocks
Review storage models, caching, queues, partitioning, replication and consistency, and load balancing. The goal is to explain when you'd use each one and what it costs, not to recite theory. If you can't say in two sentences why you'd pick one option over another, that's the topic to revisit.
2. Work prompts actively
Pick a classic prompt, such as a URL shortener, a chat app, a news feed or ride matching, and design it yourself first. Only then compare your version with a worked design. Write down what you missed, not what you liked about the answer. Those misses become your drill list.
3. Do solo timed rounds out loud
Set a 45-minute timer, open the whiteboard tool you'll use on the day, and record audio. Talk through every decision as if someone were listening. Afterward, grade the recording against the rubric further down this page. If a decision isn't on the board or in the recording, it didn't happen.
4. Move to live mocks
A live mock adds what solo practice can't: someone who interrupts, changes a constraint halfway through, and pushes on your weakest box. After the feedback, repeat the same prompt before you move to a new one. Closing a known gap teaches you more than collecting fresh prompts.
How many practice rounds?
There's no fixed number. A useful rule of thumb is to keep doing live mocks until two in a row come back with no "missing" marks at your level. Space them a few days apart so you have time to fix what the last one found, and do at least one with someone new, so you aren't just learning one person's style.
Solo, peer, senior engineer or AI: which practice to use when
Each mode is good at something different. Most people who prepare for a system design interview need a mix, shifting toward live mocks as the loop gets closer.
| Practice mode | Best for | What it misses | Use it when |
|---|---|---|---|
| Solo, recorded | Structure and pacing | Interruptions, and an honest read on depth | Early on, and between mocks |
| Peer swap (you interview each other) | Lots of reps, and learning the interviewer's side | Calibration, if your peer hasn't run real loops | The middle of your prep |
| Senior engineer who has run real loops | Calibration to the bar at your level, realistic follow-ups, a pass or fail read | Volume, since their time is limited | Once early to find gaps, then in the last weeks before the loop |
| AI mock tool | Quick reps at any hour, and checking you covered each phase | Judgment on trade-offs, and a level read you can trust | Warm-ups |
Solo rounds and AI warm-ups feel productive because nobody tells you that you missed the point. Book the harder round early enough to act on what it finds.
How to get a mock interview with a senior engineer
Most prep material skips this step, yet a software engineer mock interview with someone who has interviewed at your level is the clearest read on whether you'd pass.
Who to ask
Look for someone who has interviewed candidates recently, because the bar moves. They should be at or above the level you're targeting and in your specialty, since backend, infrastructure, mobile and ML systems rounds reward different things. Ideally they've worked at your target company or one of similar scale. For a senior software engineer mock interview, that usually means a staff engineer or an engineering manager who still interviews. A title on its own isn't enough, so ask whether they've run this kind of round.
Where to find one
Start with former tech leads and colleagues who have moved to other companies, then alumni networks, engineering communities and meetups. Paid mock-interview services are another route. Mentorship platforms that filter by company and expertise make it easier to find someone who has interviewed where you're applying.
How to ask
Keep the message short and specific, and make it easy to say yes. Adapt this:
Hi [Name], I have a [company] [level] system design round on [date]. Would you run one 45-minute mock with me and spend 15 minutes on feedback? I'll send the job description and a one-page rubric ahead of time. Please interrupt me the way a real interviewer would.
If someone says no, thank them and ask the next person.
What to send before the session
- The job description, plus your target level and the round type
- The company, and the whiteboard tool you'll use on the day
- One prompt you've already done, so they pick a new one
- Your two weakest areas, so they know where to push
- The rubric below, so they know what to mark
A 60-minute system design mock: the agenda
This agenda fits a system design mock interview, a 45-minute round plus a real debrief, into one hour. It's a suggested split for practice, not any company's rule.
| Minutes | What happens | What the interviewer does |
|---|---|---|
| 0-5 | Brief: level, company, round, what to score | Confirms the level and the rubric |
| 5-10 | Clarify requirements and scope | Answers questions, but stays a little vague, like a real interviewer |
| 10-15 | Estimate scale | Asks which numbers actually change a decision |
| 15-22 | API and data model | Probes access patterns and keys |
| 22-32 | High-level design | Lets you drive, and notes where you go quiet |
| 32-45 | Deep dive on the hardest component | Changes one constraint, such as a traffic spike, a new region or a failed dependency |
| 45-50 | Wrap-up: summary and what you'd do next | Asks what you'd build first with more time |
| 50-60 | Debrief | Marks the rubric, gives a would-pass read at your level, names one drill |
Ask the interviewer to stay in character until minute 50, with hints only of the kind a real interviewer would give, like a nudge toward a skipped requirement. The debrief is the point of the hour, so protect the last 10 minutes even if the design isn't finished.
A feedback rubric to hand your interviewer
Send this with your prep note so the interviewer knows what to watch for. Each row gets one of three marks: strong, mixed or missing. Leave out point totals. The goal is to find gaps, not to add up a score.
| Area | Strong looks like | Missing looks like |
|---|---|---|
| Scoping | Asks who uses it and what matters most, then states a short list of requirements before designing | Starts drawing in the first minute; requirements come up only when asked |
| Estimation | Rough numbers that drive a choice, like whether the data fits on one machine | Long arithmetic that never changes the design, or no numbers at all |
| Interface and data model | Clear API calls and a data model shaped by the main read and write patterns | Picks a database before saying how the data will be used |
| High-level design | A simple end-to-end path first, then components added for a stated reason | A crowded diagram with parts nobody explains |
| Deep dive and trade-offs | Goes deep on the hardest part and says what each option gives up | Shallow everywhere, or "it depends" without ever picking |
| Reliability and failure handling | Raises what breaks, how it's detected and what users see, without being prompted | Treats every component as always up |
| Communication | Narrates decisions, checks in, and recovers cleanly after a hint | Long silences, or talks without pausing for questions |
One rule makes the rubric useful: for each row, the interviewer writes down one moment from the session, such as "at about minute 20 you picked a database before stating the access pattern." A note tied to a moment is something you can fix.
End every debrief with the same two questions: "Would this pass at my level?" and "What's the one drill before next time?"
How the round differs at Google, Amazon, Meta and Microsoft
Each company runs its loop its own way, and details change, so read the company's own pages first.
- Amazon. Amazon's SDE II interview prep page says the online assessment includes systems design scenarios, the loop has four 55-minute interviews, and the Leadership Principles are evaluated throughout. Practice tying your design trade-offs to a real project story. See the Amazon software engineer interview prep page for more.
- Microsoft. The loop is several back-to-back interviews, mostly coding or design, and system design comes up for experienced roles. The Microsoft software engineer interview prep page covers the rest.
- Google. Google's How we hire pages walk through its hiring process and interview prep. Check them for the current format, and practice with Google software engineers who know the bar.
- Meta. Meta publishes a Full Loop interview guide for software engineers, which describes the onsite as several different conversations. Read it for the current round names, then practice with Meta software engineers.
For anywhere else, the rule is the same: practice with someone who has interviewed at that company or one of similar scale, such as Apple engineers if that's where you're headed.
What to bring, and what to do after
Bring the job description, the whiteboard tool you'll use on the day, a timer, the rubric, and the two areas you want pushed.
Afterward, write down your three fixes the same day. Re-run the same prompt within the week, then move to a new one. Send a short thank-you that says what you changed because of their feedback. It's the message most likely to get you a second round.
Not sure whether you need a timed mock or a broader conversation about your career? The engineering mentorship guide's mock vs career section helps you pick which kind of session to book.
Common system design practice mistakes
- Practicing silently. The round grades what you say, so talk through every rep, even alone.
- Reading the solution first. Attempt the prompt before you look, or you'll only learn to recognize answers.
- Collecting new prompts instead of repeating weak ones. Run the same prompt again until the gap a mock found is closed.
- Booking a general career chat when you need a timed mock. Say up front that you want a scored round with a debrief.
- One mock the night before the loop. Leave time to fix what it finds, so book it at least a week out.
- Over-building before the requirements are clear. Spend the first minutes on scope, and add components only when a requirement calls for them.
- Asking a senior engineer for tips. Ask them to run and score a round instead.
Practicing with a senior engineer through a mentor
A mentorship platform is one way to reach engineers who have run real loops. You can browse backend engineering mentors or software engineering mentors, or look by company, such as Amazon software engineers and Microsoft software engineers. For the behavioral part of a loop, interview coaching is a better fit.
If you'd like a senior engineer to run your next practice round, you can browse mentors on ADPList and filter by company and by expertise such as backend engineering. Send the job description and your target level when you book, and ask for a timed round plus a debrief. Mentorship is free to start.
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Frequently asked questions
How do I practice for a system design interview?
Learn the core building blocks first, such as storage, caching, queues, partitioning and consistency. Then attempt common prompts on your own before reading a worked solution, with a timer running and talking out loud. Once a solo round feels structured, switch to live mocks with someone who interrupts and pushes back, and repeat the same prompt after feedback until the gaps close.
How do I get a mock interview with a senior engineer?
Look for an engineer who has recently run interviews at the level you're targeting, ideally in your specialty, such as backend or infrastructure. Former tech leads, alumni networks, engineering communities, paid mock-interview services and mentorship platforms are common places to find one. Ask for one timed round plus a debrief, and send the job description and your target level ahead.
How many mock interviews should I do before a system design interview?
There is no fixed number. A practical rule is to keep doing live mocks until two rounds in a row come back with no "missing" marks on your rubric at the level you're interviewing for. Space them a few days apart so you can fix what the last one found, and do at least one with someone you haven't practiced with before.
Can I practice system design interviews alone?
Yes, for part of your prep. Solo rounds build structure: set a timer, pick a prompt, talk out loud, record yourself, then grade the recording against a rubric. What solo practice can't give you is an interruption, a constraint that changes mid-round, or an honest read on whether your depth matches the level. Add live mocks with a person before the real loop.
What should feedback from a system design mock include?
Good feedback names a moment, not a vibe. Ask for a mark on each part of the round, from scoping and estimation to the deep dive, trade-offs, failure handling and communication, with one example from the session for each. It should end with a clear read on whether you'd pass at your target level and the one drill to do before the next round.
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