← Articulet System Design, Made Clear Diagnostic
20 minutes Before Chapter 1

Diagnostic and track routing.

Find your real bottleneck before adding more content.

Outcome
Route yourself into the right path: foundations, interview structure, scale practice, communication, recovery, or senior-level trade-offs.
Part 1

Baseline system answer.

Timer: 10 minutes
Design a URL shortener for 10 million daily active users.
  • Ask at least three clarifying questions.
  • Estimate read and write shape.
  • Draw the first-pass architecture.
  • Name one deep dive and one trade-off.
Part 2

Concept checks.

Cache

When is a cache justified?

  • Repeated reads
  • Acceptable staleness
  • Clear invalidation story
Queue

What belongs off the request path?

  • Slow side effects
  • Retryable work
  • Batchable processing
Data

What is the primary access pattern?

  • Lookup by key
  • Relationship query
  • Append and scan
Scale

What grows first?

  • Users
  • Content
  • Fan-out
Consistency

Where must correctness be strong?

  • Payments
  • Identity and auth
  • Durable acceptance
Recovery

What do you say when stuck?

  • Name the issue
  • Restate the scope
  • Continue with a smaller step
Part 3

Spoken opener.

Timer: 90 seconds
Open the URL shortener answer out loud.
  • State the answer structure.
  • Ask the first two clarifying questions.
  • Say what you will estimate and why.
Show a strong opener shape
I will first scope the core product behavior, estimate rough create and redirect traffic, sketch a baseline with a mapping store and redirect path, then go deeper on unique code generation and caching because those are likely to drive correctness and latency.
Routing

Score the diagnostic, then pick a path.

Total scoreRouteDo nextReason
0-11 Foundations Chapters 1-8 slowly, one diagram per chapter. You need vocabulary, access patterns, and baseline shapes before mocks.
12-18 Interview structure Chapters 1-3 plus rubric practice. You may know pieces but need a more reliable answer structure under pressure.
19-25 Scale and trade-offs Chapters 9-18 plus spaced review. The baseline is present, but bottleneck choice and justification need work.
26-32 Mock interview Timed mocks and capstones. You need performance pressure, feedback, and polish.