The best investment is in yourself
One level up pays $109,000 to $135,000 more a year at Google, Meta and Amazon. If a month of Pro ($49) helps you land it, that is over 2,000 times its price back in the first year.
Monthly
For one focused interview loop: every mock and the AI Mentor while it lasts.
Annual
Save 75 %A year for the price of three months. For prep that runs over months.
Lifetime
Every mock and the AI Mentor, and every question added later, for good.
Payments are handled by Stripe. Subscriptions can be cancelled from the billing portal at any time. A first purchase can be refunded within 7 days if you have started fewer than 3 mock interviews; see the refund policy.
Why one level is worth $109,000 to $135,000 a year
Interviewers ask the same system design question at every level and grade it to a different bar (what each level is expected to show), so this round weighs heavily in the level you are offered. That level is in every paycheck after it.
A year of Pro costs $147, less than half a day of the smallest of these differences. Pro will not give the answer for you. It is where you give it out loud, to an interviewer who pushes back, until it sounds like the level you want.
- Google L4 → L5+$109,000a year
- Meta E4 → E5+$135,000a year
- Amazon L5 → L6+$111,000a year
Median total yearly compensation (salary, stock and bonus) of US software engineers on Levels.fyi, checked 2 November 2026: Google L4 $304,165, L5 $412,858; Meta E4 $312,037, E5 $447,170; Amazon L5 $274,364, L6 $385,379. Medians move as people add data, and they describe the market, not what any one offer will be.
What a Pro round gives you
An example round on Design a URL Shortener, written to show the format. The interviewer follows what you say and draw, so no two rounds go the same way.
The interviewer probes what you say
Then debriefs you, stage by stage
A solid first half: you pinned the read-to-write ratio early, and a cache-first redirect path would hold the load. The round slipped in the deep dives: code generation stayed vague until I pushed, and you never said what happens to click counts when the stream falls behind. At senior level this reads as a lean hire that one stronger deep dive would turn into a clear one.
Strong: Read-to-write ratio and peak QPS before any boxes · Cache-first redirect with the 301 vs 302 trade-off · Idempotent create in the API
Missing: No plan for collisions or guessable codes · Edit consistency relied on purges succeeding · Analytics lag and replay not covered
Next: Practise the key generation deep dive: a ranged counter with a scrambled base62 encoding, and what it costs compared with random codes and retries.
- Requirements. Clear scope with expiry and abuse controls named; custom aliases came late. See how the reference candidate did it →
- Estimates. Right order of magnitude for redirects per second and storage, with the derivation said out loud. See how the reference candidate did it →
- High-level design. Good read path; the write path skipped how a code is reserved before it is returned. See how the reference candidate did it →
- Deep dives. The hot-key answer was strong; key generation and analytics needed prompting. See how the reference candidate did it →
What is free, and what Pro adds
| Feature | No account | Free account | Pro |
|---|---|---|---|
| Walkthroughs of strong answers | Up to the deep dives; URL Shortener in full | All 83, in full | All 83, in full |
| Reference designs, study guides, interactive concepts | |||
| AI mock interviews | Hear the interviewer open the round | Hear the interviewer open the round | Every question, timed or untimed |
| Scored debrief, stage by stage | – | – | After every round |
| Company-style rounds (Google, Meta, Amazon…) | The opening | The opening | Every company |
| AI Mentor | Suggested questions | Suggested questions | Live questions, any time |
| Transcripts, debriefs and progress saved | – |
A year of Pro costs less than one hour with a human interviewer
A mock interview with a human expert usually costs $100 to $400 for a single session. Pro is $147 a year for a round on any question, any day, at two in the morning if that is when you practise.
The two work well together: practise here until the structure, the numbers and the deep dives come without thinking, then spend on one human mock interview before the onsite.
Questions about plans
Something else? Email support@sysdesignprep.com.
Can I try Pro before paying?
You can see what you would be buying first. Every walkthrough is free with a Google sign-in, so you can watch a strong candidate answer any question in full; the AI Mentor’s suggested answers are free; and anyone can start a mock interview and hear the AI interviewer open the round. Answering it, and live questions to the AI Mentor, are Pro. A first purchase can be refunded within 7 days if you have started fewer than 3 mock interviews.
What does Pro include?
AI mock interviews on every question, timed or with the AI Mentor, each ending in a scored debrief; live questions to the AI Mentor, including comparing your answers with the candidate’s; and the company-style mock interviews (Google, Meta, Amazon, OpenAI and others). Every question added later is included, and a daily fair-use limit on AI messages keeps it fast for everyone. All three plans include the same thing; they differ only in how you pay.
What is free?
Every walkthrough, with no account, up to its deep dives, including the AI Mentor’s suggested questions. Design a URL Shortener is free in full. Sign in with Google and every other walkthrough is free in full too. On a mock interview, anyone can hear the interviewer open the round. The study guides, the interactive concepts, the reference designs and which companies ask each question are free too. Pro adds the AI mock interviews and live questions to the AI Mentor.
Does the subscription renew automatically?
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.
Can I upgrade from monthly to annual or lifetime?
Yes. Open the billing portal from the pricing page and switch plans; Stripe prorates the unused part of the current period.
Is there a refund policy?
Yes, on a first purchase. Email us within 7 days of it, having 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.