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Adaptive system design practice

DeckedBeta

Daily system design practice for your next interview.

Practice system design trade-offs in short daily sessions

Preparing for a system design interview? Solve short architecture scenarios, compare the wiring, and revisit your weakest topics. Start free, without an account.

Free: up to 100 questions per UTC day from existing cards. Fresh AI generation requires Pro. Your allowance resets at midnight UTC.

How practice works
  1. Read the scenario. e.g. "A client pushes 1,000 events/s to a downstream service."
  2. Pick an approach. 2-4 options; one fits the constraints best.
  3. Learn the trade-offs. Every card explains why the winner wins and the rest fail.
  4. Study adaptively. Sessions target your weakest topics, and spaced repetition resurfaces cards before you forget.
How cards are made

Cards are generated with AI assistance and cached for reuse. Automatic checks verify required fields, answer labels, and diagram connections before accepting a generated card; they do not verify technical accuracy. Explanations can be wrong. Use “Report an explanation” after answering to send the card details for review. Saved cards remain available for offline review, with seed cards as a fallback.

Privacy & your data

No account required. Progress is saved in your browser and synchronized with the server using a device identifier, or your account when signed in. Custom cards, bookmarks, and session resume state stay in this browser. Fresh card requests also go through the server.

Try a trade-off

An upload takes 20 seconds to process. Where should the work happen?

Your API must acknowledge accepted uploads within 300 ms. Files must survive worker restarts, and users can check processing status later.

  1. Process the file inside the API request.
  2. Store the file durably, enqueue a job, and let a worker process it.
  3. Return success, then start an in-memory background task in the API process.
Your progress, Concept Lab & tools
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Progressive challenge

Level 1 · Foundations

Name the right building block.

Next: build evidence with your first session.

    Concept lab: make a prediction, then see the system respond.

    ✦ Daily Goal cards

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    Explore · choose · test

    Concept Lab

    Choose a system-design idea, grouped by area, to open its explanation and pressure test on one child page.

    The map of ideas, by area

    What do you want to understand?

    Concepts are grouped by area. Larger words reflect connections and study coverage as a discovery hint, not a ranking or a gate.

    Sandbox experiments are prepared in the background.

    Create a Card

    Write your own system design scenario to add to the deck.

    Topics to know first
    1 / 8
    Topic ★★★ Level 1 · Foundations

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    System design

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    Topic Map

    Choose any topic to practice. Prerequisites show the expected background, not locked content.

    Understand · test · explain

    Concept Lab

    Read the concept on one side, change a constraint on the other, and keep both views in context. Everything is deterministic and educational — it never connects to infrastructure.

    Side A · Understand

    Concept Wiki

    Find the idea, trade-off, or failure mode behind the experiment.

    Side B · Test

    Concept Sandbox

    Make a prediction, change one assumption, and observe the modeled result.

    0 / 5 situations complete

    Level 1

    Choose a situation

    Focus:

    Make your prediction

    Make a prediction before you run the model.

    Change an assumption, choose the outcome you expect, then run the experiment to see the causal chain.

    Model boundary: these outputs are teaching signals based on the assumptions shown below each result, not production capacity recommendations or vendor benchmarks.

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    Reference · compare · decide

    Design Decisions

    The recurring architecture trade-offs behind real systems. Each decision compares the viable options across the criteria that matter, then records the choice and why it wins.

    Reference · compare · decide

    Design Decisions

    One architecture decision, its trade-offs, and where to read and practice more.

    Concept Wiki

    Send Feedback

    Found a confusing card, a bug, or a feature you'd love? Your note is recorded for review. When issue tracking is available, it is also filed as a project issue.

    System Design Flashcards · Beta