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Learn it. Practise it. Prove it.

System design has no answer key. So we built a loop. Learn one idea, practise it under real load, and prove it in a mock interview with an honest verdict.

Try the DrillPlay Level 1, no sign-up

Free to start. No credit card required.

The loop

Six parts, one path

Start anywhere. Every part has its own page, and you can read all of them without an account.

  1. 01

    Learn

    Take in one idea at a time, in plain English.

  2. 02

    Practise

    Use it. Build it, break it, and do it every day.

  3. 03

    Prove

    Take a real round and see an honest verdict.

01 · Learn · Course and AI tutor

Learn from zero, in plain English

125 lessons in 19 modules, every one free to read. Each lesson uses only ideas you have already met. An AI tutor (free account) sits beside you and answers in your own words.

  • Ask the moment you are stuck

    The tutor sits next to the lesson. No forum, no waiting. It will not write your interview answer for you.

  • Easy English, on purpose

    Short sentences and common words. Every new term is explained the first time you see it.

See the course

02 · Practise · 7-minute Drill

Seven minutes, every day

Today’s Drill is one real situation. An AI interviewer asks you 3 to 5 questions, one at a time. You answer in your own words and get a short report.

  • Today’s Drill

    The same Drill for everyone, new each day, and free. Read today’s Drill.

  • Incident investigations

    About 12 minutes. Read dashboards and logs, find the cause, and fix it.

See how the Drill works

03 · Practise · Load simulator

See what breaks before an interviewer asks

A free system-design simulator with 8 levels, from one server to two regions. Build the design, run real load, and read exactly where it gives up. No AI, no credits.

  1. 01

    Work out the traffic

    Start with the numbers: requests per second, how many are reads, how much data. Small sums, shown step by step.

  2. 02

    Build your design

    Choose the parts: load balancer, app servers, cache and database. Set how big each one is.

  3. 03

    Run it under real load

    Add users until something breaks. You see the exact moment, and the part that gave up.

  4. 04

    Get an honest verdict

    A clear answer against your target level, with the one thing to fix next.

Play Level 1See the simulatorFree. No sign-up needed.

04 · Practise · Problems and cost lab

Real problems, and a free bill lab

  • Real problems and Prove it

    From a URL shortener to ticket booking with a Tatkal rush. Open a problem, design it on a whiteboard, then run a real load test on your own design.

  • Cloud cost lab

    Interviewers ask what a design costs each month. Build a cloud bill for real-looking workloads, read it line by line, and hit the budget. It is free and runs in your browser.

    Open the cost lab

  • Review your mistakes

    A few minutes a day. Each card is a point you missed in your own reports. If you get it, it comes back later. If not, it comes back tomorrow.

See problems and the cost lab

05 · Prove · Mock interviews

The real round, before the real one

Four rounds with an AI interviewer, so you can practise the round you are actually facing.

  1. 01System designProve it

    25 to 45 minutes. Whiteboard it, or load-test it. “Prove it” runs a real load test on your own diagram.

  2. 02Machine codingPython · Java · JavaScript · C++

    60 to 90 minutes. Design the classes, code a working core, then handle a new requirement. Hidden tests run on your code.

  3. 03Resume grilling

    About 35 minutes. Paste your resume. The interviewer digs into your own projects, then tells you how convincing you were.

  4. 04Incident

    12 to 15 minutes. Read dashboards and logs, find the cause, and stop the damage before the clock runs out.

Every round ends with a report judged against your target level: a verdict, a score for each area, and what a stronger answer would add.

See the four rounds

06 · Prove · Technical Passport

Show your work, not a certificate

Pick the practice reports you want and send one link to a recruiter or a friend. They see what happened and the proof behind it.

  • Off until you turn it on

    You choose each report. Switch it off and the link stops working at once.

  • Never your code or your chat

    No email, no phone, no code, no chat, and no hidden tests are shown.

See the Passport

What is free

Start without paying

Paid plans are one payment. Nothing renews, and you see the price before you pay.

  • All 125 lessons, free to read with no account
  • Simulator: all 8 levels, with no sign-up
  • Cost lab, in your browser
  • 1 Drill and 1 redo a day
  • 20 AI tutor questions a day
  • 1 AI interview and 1 AI system-design session
See pricing

Is Tradeoff right for you?

We built this for serious preparation. Make sure it is a fit.

This is for you if

  • You are preparing for SDE-1, SDE-2 or Senior interviews
  • You want structure, not content overload
  • You value honest feedback and a clear view of how ready you are

This is not for you if

  • You are casually exploring coding
  • You want shortcuts without practice
  • You are not preparing for a system design round

Know where your design breaks

Start free. Upgrade only when you are sure.

Try the DrillPlay Level 1, no sign-up