How to use these notes

These are my own interview-prep notes, not a course. The system-design track is the main part. The company tabs are prep plans for specific loops (Mercor, DoorDash). Low-level design and DSA are smaller and still growing.

What a design interview is actually grading

You are given a fuzzy product and about 45 minutes. The interviewer is not waiting for a secret diagram. They are watching whether you can narrow the problem, propose a design that meets the contract you just wrote, and then go deep on the part that is actually hard. Four habits show up on almost every rubric, whatever the company calls them:

• Navigation. You pick the three features that matter and you do not drown in the rest.
• Design. The pieces fit. A request can be walked from the client to storage and back.
• Technology judgment. You name a real datastore, a real index, and the cost of that choice.
• Collaboration. You take a hint, you draw without being asked, and you state what breaks.

Mid-level candidates are expected to finish a coherent design. Senior candidates should get there quickly enough to spend the second half on one hard problem: ranking, hot keys, exactly-once side effects, or model cost. Staff conversations add scope, migration, and organizational constraints. You do not need a different framework for each level. You need the same framework, run faster, with a deeper second half.

How the track is organized

Read Delivery until the clock is automatic. Then skim a core concept only when a problem forces it. Technologies are reference pages: Postgres, Redis, Kafka, and the rest, written so you can defend a choice in two minutes. Patterns are the moves you reuse (fan-out, sagas, claim-with-lease). Worked problems are the reps.

Each page ends with a few callouts and a quiz. The failure-mode callout is the list you should be able to recite. “Say this” is phrasing, not a script to memorize word for word. “Gaps” is what the free public guides tend to skip. Quizzes are all unlocked. Multiple choice is scored in this browser. Short answers reveal when you click.

A study loop that fits a job and a semester

One hour is enough if it is deliberate.

1. Pick one problem. Set a timer for 25 minutes. Talk out loud. Draw on paper or Excalidraw. Stop when the timer ends, even if the design is incomplete.
2. Spend 15 minutes comparing your drawing to the worked problem. Write down the one gap, not ten.
3. Spend 10 minutes on the concept page that gap points at. Do the quiz.

Do not highlight. Do not watch a second explanation of the same diagram. The failure mode of interview prep is consuming material you cannot reproduce.

Before a company loop, open that company’s tab and do the rounds in order, including the stories. Do not invent a metric in the room.

What this site will not do

No login, nothing sent anywhere. Progress is localStorage. Search is an index built with the static site. A new page is a markdown file, and a new track is one more entry in src/content/tracks.json.