← Articulet System Design, Made Clear Timed mocks
Simulation layer After Parts 1, 3, 4, and 5

Timed mock interviews.

Train the shape of a real answer, not just isolated concepts.

Outcome
You can answer under time pressure, handle follow-ups, recover from mistakes, and close with explicit trade-offs.
Mock ladder

Four formats, increasing pressure.

10 minutes

Mini mock

  • Opening structure
  • Clarifying questions
  • One design implication
25 minutes

Focused mock

  • Scope, size, sketch
  • One deep dive
  • One recovery moment
45 minutes

Full interview

  • Complete answer flow
  • Interviewer follow-ups
  • Final trade-off summary
60 minutes

Senior/staff mock

  • Reliability and operations
  • Cost and migration path
  • Multiple valid options defended
Full mock format

45-minute interview timing.

0-5

Clarify

Define users, core actions, scope boundaries, latency, reliability, and scale assumptions.

5-10

Estimate

Calculate only the numbers that affect architecture: read QPS, write QPS, peak, storage, and fan-out.

10-20

Sketch

Draw the baseline with user path, data path, stores, cache, async side work, and one clear bottleneck.

20-35

Deep dive

Choose the subsystem where scale, correctness, or reliability pressure is highest.

35-42

Follow-ups

Handle one changed constraint and one failure scenario without losing the answer structure.

42-45

Close

Summarize the design, name trade-offs, and say where the system evolves next.

Mock bank

Use these prompts in rotation.

Compact

Rate limiter

  • Follow-up: limits must work across regions.
  • Failure: shared counter store is slow.
Read-heavy

News feed

  • Follow-up: celebrities have huge fan-out.
  • Failure: ranking service is unavailable.
Realtime

Chat system

  • Follow-up: offline delivery and ordering.
  • Failure: websocket server disconnects.
Async

Video upload

  • Follow-up: transcoding backlog grows.
  • Failure: one processing stage fails.
Reliability

Notification system

  • Follow-up: channel preferences and retries.
  • Failure: push provider is down.
Starter

URL shortener

  • Follow-up: custom aliases and expiration.
  • Failure: one link goes viral.