Is 30 days enough to prepare for a system design interview?

For most rounds, yes, at about an hour a day. Days 1 to 10 give you the building blocks every answer uses. Days 11 to 28 walk through real systems the way an interviewer wants them. Three mock interviews show you where you are weak while there is still time to fix it.

How do the mock interviews work?

The AI tutor plays the interviewer. It asks one question at a time, stage by stage: requirements, estimation, API and data model, high-level design, deep dive, reliability and wrap-up. At the end you get a score from 1 to 5 on ten points, each with quotes from your own answers, and three lessons to read next.

What if I miss a day?

Carry on from where you stopped. When you are signed in, this page marks the lessons you finished and shows the next one to read.

How is this different from the free 30-day study plan?

The free plan covers the whole subject by topic. This path is for an interview: it names the exact lessons and guides for each day, and it adds the mock interviews.

A day-by-day plan · System Design

Interview in 30 Days

For anyone with a system design round already on the calendar. You have a framework for any design question, you have walked through twelve common systems, and you have done three timed mock interviews with scorecards.

30 days
50 lessons
7 free
13 interview guides
3 mock interviews
28 hours of reading

Start with Latency

Who it is for

Anyone with a system design round already on the calendar.

What you can do at the end

You have a framework for any design question, you have walked through twelve common systems, and you have done three timed mock interviews with scorecards.

First milestone

Finish the framework (days 1 to 10), ten common systems, and three mock interviews.

Day 28: Mock interview 3

7 of the 50 lessons are free to read now, with no account. The other 43 are in the System Design Masterclass course: $49 once, lifetime access, pay with PayPal.

Get System Design · $49

The plan, day by day

Times are each lesson’s own reading time, added up. A mock interview is set to 45 minutes. A lock means the lesson is in the course.

Day 1
The numbers
41 min
Learn the three numbers every design is judged by.
1. LatencySystem Design lesson14 minfree
2. ThroughputSystem Design lesson10 minfree
3. BandwidthSystem Design lesson17 minfree
Day 2
Scaling
82 min
Know when to buy a bigger machine and when to add more machines.
1. ScalabilitySystem Design lesson20 minin the course
2. Horizontal ScalingSystem Design lesson32 minin the course
3. Stateless vs Stateful SystemsSystem Design lesson30 minin the course
Day 3
Getting traffic in
106 min
Explain DNS, load balancers and proxies in one breath.
1. DNS (Domain Name System)System Design lesson40 minfree
2. Load BalancingSystem Design lesson34 minin the course
3. Reverse ProxySystem Design lesson32 minin the course
Day 4
Caching
79 min
Put a cache in front of a database and say what goes wrong.
1. CachingSystem Design lesson30 minin the course
2. Cache Eviction PoliciesSystem Design lesson24 minfree
3. Cache InvalidationSystem Design lesson25 minfree
Day 5
Choosing a database
68 min
Pick SQL or NoSQL for a reason you can say out loud.
1. SQL vs NoSQLSystem Design lesson42 minin the course
2. Database IndexingSystem Design lesson26 minin the course
Day 6
Spreading data out
80 min
Copy data for reads and split it for writes.
1. Database ReplicationSystem Design lesson20 minin the course
2. Database ShardingSystem Design lesson35 minin the course
3. Consistent HashingSystem Design lesson25 minin the course
Day 7
Queues
60 min
Move slow work out of the request.
1. Asynchronous ProcessingSystem Design lesson18 minfree
2. Message QueuesSystem Design lesson20 minin the course
3. Pub/Sub PatternSystem Design lesson22 minin the course
Day 8
APIs that hold up
78 min
Design an API that survives retries and abuse.
1. REST APISystem Design lesson28 minin the course
2. IdempotencySystem Design lesson28 minin the course
3. Rate LimitingSystem Design lesson22 minin the course
Day 9
Consistency
45 min
Say what a user can see after a write, and why.
1. CAP TheoremSystem Design lesson25 minin the course
2. Data Consistency ModelsSystem Design lesson20 minin the course
Day 10
Edges and the framework
84 min
Finish the building blocks, then see the full interview framework on one API.
1. Content Delivery Network (CDN)System Design lesson26 minin the course
2. API GatewaySystem Design lesson28 minin the course
3. Design Public APIinterview guide, free30 minfree
Day 11
System 1: URL shortener
73 min
The classic read-heavy system.
1. Design Tiny URL Shortenerinterview guide, free8 minfree
2. Design a URL ShortenerSystem Design lesson65 minin the course
Day 12
System 2: rate limiter
58 min
Count requests across many servers.
1. Design Rate Limiterinterview guide, free40 minfree
2. Token Bucket AlgorithmSystem Design lesson18 minin the course
Day 13
System 3: chat
30 min
Deliver a message to someone who may be offline.
1. Design WhatsAppinterview guide, free8 minfree
2. WebSocketsSystem Design lesson22 minin the course
Day 14
Mock interview 1
45 min
Your first timed mock. Read the scorecard slowly.
1. Mock interview: design Tiny URL ShortenerAI interviewer, mid-level level45 min
Day 15
System 4: news feed
28 min
Build a timeline for millions of followers.
1. Design Twitterinterview guide, free8 minfree
2. Fan-Out/Fan-InSystem Design lesson20 minin the course
Day 16
System 5: notifications
38 min
Send to every device, once, even when parts fail.
1. Design Notification Systeminterview guide, free20 minfree
2. At-Least-Once DeliverySystem Design lesson18 minin the course
Day 17
System 6: video
22 min
Store and stream large files around the world.
1. Design YouTubeinterview guide, free8 minfree
2. Object StorageSystem Design lesson14 minin the course
Day 18
System 7: ride matching
25 min
Find nearby drivers fast.
1. Design Uberinterview guide, free9 minfree
2. Geospatial IndexingSystem Design lesson16 minin the course
Day 19
System 8: file sync
87 min
Keep one folder the same on many devices.
1. Design Dropboxinterview guide, free17 minfree
2. Design a File Storage System like DropboxSystem Design lesson70 minin the course
Day 20
When things fail
105 min
Retries, timeouts and circuit breakers: the follow-up questions.
1. Retry PatternsSystem Design lesson35 minin the course
2. Timeout PatternsSystem Design lesson35 minin the course
3. Circuit Breaker for ResilienceSystem Design lesson35 minin the course
Day 21
Mock interview 2
45 min
A harder problem. Compare this scorecard with the first one.
1. Mock interview: design Rate LimiterAI interviewer, mid-level level45 min
Day 22
System 9: search box
35 min
Suggest words as the user types.
1. Design Search Autocompleteinterview guide, free17 minfree
2. Inverted IndexSystem Design lesson18 minin the course
Day 23
System 10: payments
66 min
Never charge a customer twice.
1. Design Payment Systeminterview guide, free18 minfree
2. Idempotency KeysSystem Design lesson18 minin the course
3. Saga PatternSystem Design lesson30 minin the course
Day 24
System 11: web crawler
38 min
Crawl billions of pages politely.
1. Design Web Crawlerinterview guide, free16 minfree
2. Bloom FiltersSystem Design lesson22 minin the course
Day 25
System 12: ticket booking
50 min
Sell one seat to exactly one person.
1. Design Ticketmasterinterview guide, free20 minfree
2. Distributed LocksSystem Design lesson30 minin the course
Day 26
Seeing inside a system
52 min
Answer the question: how would you know it is broken?
1. Four Golden SignalsSystem Design lesson12 minin the course
2. Distributed TracingSystem Design lesson25 minin the course
3. SLO (Service Level Objectives)System Design lesson15 minin the course
Day 27
Leaders and lag
88 min
The deep-dive topics senior interviewers like.
1. Replication LagSystem Design lesson18 minin the course
2. Leader ElectionSystem Design lesson35 minin the course
3. Consensus AlgorithmsSystem Design lesson35 minin the course
Day 28
Mock interview 3
45 min
The real-time system, at a higher level.
milestone: Finish the framework (days 1 to 10), ten common systems, and three mock interviews.
1. Mock interview: design WhatsAppAI interviewer, senior level45 min
Day 29
Fix your weakest points
25 min
Open your three scorecards and read the lessons each one recommends.
1. Your past scorecards, with the lessons each one recommends · Open my scorecards
2. Graceful DegradationSystem Design lesson25 minin the course
Day 30
The company you are interviewing at
Read the guide closest to the company, then rest.
1. Find the company's own system among the interview guides · Browse the interview guides

Questions about this path

Is 30 days enough to prepare for a system design interview?: For most rounds, yes, at about an hour a day. Days 1 to 10 give you the building blocks every answer uses. Days 11 to 28 walk through real systems the way an interviewer wants them. Three mock interviews show you where you are weak while there is still time to fix it.
How do the mock interviews work?: The AI tutor plays the interviewer. It asks one question at a time, stage by stage: requirements, estimation, API and data model, high-level design, deep dive, reliability and wrap-up. At the end you get a score from 1 to 5 on ten points, each with quotes from your own answers, and three lessons to read next.
What if I miss a day?: Carry on from where you stopped. When you are signed in, this page marks the lessons you finished and shows the next one to read.
How is this different from the free 30-day study plan?: The free plan covers the whole subject by topic. This path is for an interview: it names the exact lessons and guides for each day, and it adds the mock interviews.

This path runs through the System Design course. Here is the whole course, at your price.

The course this path is part of

System Design Masterclass

770 lessons · about 283 hours · 18 free to read

$49 once, lifetime access · pay with PayPal

Get System Design · $49 Read 18 lessons free first

Also from me

AI Engineering

204 lessons · about 211 hours · 10 free to read

$49 once, lifetime access · pay with PayPal

Get AI Engineering · $49 Read 10 lessons free first

Either course includes the AI tutor beside every lesson, 10 questions a day, and the full seven-stage mock interview. Try a mock interview

Other paths

System Design Foundations Senior/Staff Depth AI Engineer Foundations Production Agents

A day-by-day plan · System Design

Interview in 30 Days

30 days
50 lessons
7 free
13 interview guides
3 mock interviews
28 hours of reading

Start with Latency

Who it is for

Anyone with a system design round already on the calendar.

What you can do at the end

You have a framework for any design question, you have walked through twelve common systems, and you have done three timed mock interviews with scorecards.

First milestone

Finish the framework (days 1 to 10), ten common systems, and three mock interviews.

Day 28: Mock interview 3

7 of the 50 lessons are free to read now, with no account. The other 43 are in the System Design Masterclass course: $49 once, lifetime access, pay with PayPal.

Get System Design · $49

The plan, day by day

Times are each lesson’s own reading time, added up. A mock interview is set to 45 minutes. A lock means the lesson is in the course.

Day 1
The numbers
41 min
Learn the three numbers every design is judged by.
1. LatencySystem Design lesson14 minfree
2. ThroughputSystem Design lesson10 minfree
3. BandwidthSystem Design lesson17 minfree
Day 2
Scaling
82 min
Know when to buy a bigger machine and when to add more machines.
1. ScalabilitySystem Design lesson20 minin the course
2. Horizontal ScalingSystem Design lesson32 minin the course
3. Stateless vs Stateful SystemsSystem Design lesson30 minin the course
Day 3
Getting traffic in
106 min
Explain DNS, load balancers and proxies in one breath.
1. DNS (Domain Name System)System Design lesson40 minfree
2. Load BalancingSystem Design lesson34 minin the course
3. Reverse ProxySystem Design lesson32 minin the course
Day 4
Caching
79 min
Put a cache in front of a database and say what goes wrong.
1. CachingSystem Design lesson30 minin the course
2. Cache Eviction PoliciesSystem Design lesson24 minfree
3. Cache InvalidationSystem Design lesson25 minfree
Day 5
Choosing a database
68 min
Pick SQL or NoSQL for a reason you can say out loud.
1. SQL vs NoSQLSystem Design lesson42 minin the course
2. Database IndexingSystem Design lesson26 minin the course
Day 6
Spreading data out
80 min
Copy data for reads and split it for writes.
1. Database ReplicationSystem Design lesson20 minin the course
2. Database ShardingSystem Design lesson35 minin the course
3. Consistent HashingSystem Design lesson25 minin the course
Day 7
Queues
60 min
Move slow work out of the request.
1. Asynchronous ProcessingSystem Design lesson18 minfree
2. Message QueuesSystem Design lesson20 minin the course
3. Pub/Sub PatternSystem Design lesson22 minin the course
Day 8
APIs that hold up
78 min
Design an API that survives retries and abuse.
1. REST APISystem Design lesson28 minin the course
2. IdempotencySystem Design lesson28 minin the course
3. Rate LimitingSystem Design lesson22 minin the course
Day 9
Consistency
45 min
Say what a user can see after a write, and why.
1. CAP TheoremSystem Design lesson25 minin the course
2. Data Consistency ModelsSystem Design lesson20 minin the course
Day 10
Edges and the framework
84 min
Finish the building blocks, then see the full interview framework on one API.
1. Content Delivery Network (CDN)System Design lesson26 minin the course
2. API GatewaySystem Design lesson28 minin the course
3. Design Public APIinterview guide, free30 minfree
Day 11
System 1: URL shortener
73 min
The classic read-heavy system.
1. Design Tiny URL Shortenerinterview guide, free8 minfree
2. Design a URL ShortenerSystem Design lesson65 minin the course
Day 12
System 2: rate limiter
58 min
Count requests across many servers.
1. Design Rate Limiterinterview guide, free40 minfree
2. Token Bucket AlgorithmSystem Design lesson18 minin the course
Day 13
System 3: chat
30 min
Deliver a message to someone who may be offline.
1. Design WhatsAppinterview guide, free8 minfree
2. WebSocketsSystem Design lesson22 minin the course
Day 14
Mock interview 1
45 min
Your first timed mock. Read the scorecard slowly.
1. Mock interview: design Tiny URL ShortenerAI interviewer, mid-level level45 min
Day 15
System 4: news feed
28 min
Build a timeline for millions of followers.
1. Design Twitterinterview guide, free8 minfree
2. Fan-Out/Fan-InSystem Design lesson20 minin the course
Day 16
System 5: notifications
38 min
Send to every device, once, even when parts fail.
1. Design Notification Systeminterview guide, free20 minfree
2. At-Least-Once DeliverySystem Design lesson18 minin the course
Day 17
System 6: video
22 min
Store and stream large files around the world.
1. Design YouTubeinterview guide, free8 minfree
2. Object StorageSystem Design lesson14 minin the course
Day 18
System 7: ride matching
25 min
Find nearby drivers fast.
1. Design Uberinterview guide, free9 minfree
2. Geospatial IndexingSystem Design lesson16 minin the course
Day 19
System 8: file sync
87 min
Keep one folder the same on many devices.
1. Design Dropboxinterview guide, free17 minfree
2. Design a File Storage System like DropboxSystem Design lesson70 minin the course
Day 20
When things fail
105 min
Retries, timeouts and circuit breakers: the follow-up questions.
1. Retry PatternsSystem Design lesson35 minin the course
2. Timeout PatternsSystem Design lesson35 minin the course
3. Circuit Breaker for ResilienceSystem Design lesson35 minin the course
Day 21
Mock interview 2
45 min
A harder problem. Compare this scorecard with the first one.
1. Mock interview: design Rate LimiterAI interviewer, mid-level level45 min
Day 22
System 9: search box
35 min
Suggest words as the user types.
1. Design Search Autocompleteinterview guide, free17 minfree
2. Inverted IndexSystem Design lesson18 minin the course
Day 23
System 10: payments
66 min
Never charge a customer twice.
1. Design Payment Systeminterview guide, free18 minfree
2. Idempotency KeysSystem Design lesson18 minin the course
3. Saga PatternSystem Design lesson30 minin the course
Day 24
System 11: web crawler
38 min
Crawl billions of pages politely.
1. Design Web Crawlerinterview guide, free16 minfree
2. Bloom FiltersSystem Design lesson22 minin the course
Day 25
System 12: ticket booking
50 min
Sell one seat to exactly one person.
1. Design Ticketmasterinterview guide, free20 minfree
2. Distributed LocksSystem Design lesson30 minin the course
Day 26
Seeing inside a system
52 min
Answer the question: how would you know it is broken?
1. Four Golden SignalsSystem Design lesson12 minin the course
2. Distributed TracingSystem Design lesson25 minin the course
3. SLO (Service Level Objectives)System Design lesson15 minin the course
Day 27
Leaders and lag
88 min
The deep-dive topics senior interviewers like.
1. Replication LagSystem Design lesson18 minin the course
2. Leader ElectionSystem Design lesson35 minin the course
3. Consensus AlgorithmsSystem Design lesson35 minin the course
Day 28
Mock interview 3
45 min
The real-time system, at a higher level.
milestone: Finish the framework (days 1 to 10), ten common systems, and three mock interviews.
1. Mock interview: design WhatsAppAI interviewer, senior level45 min
Day 29
Fix your weakest points
25 min
Open your three scorecards and read the lessons each one recommends.
1. Your past scorecards, with the lessons each one recommends · Open my scorecards
2. Graceful DegradationSystem Design lesson25 minin the course
Day 30
The company you are interviewing at
Read the guide closest to the company, then rest.
1. Find the company's own system among the interview guides · Browse the interview guides

Questions about this path

Is 30 days enough to prepare for a system design interview?: For most rounds, yes, at about an hour a day. Days 1 to 10 give you the building blocks every answer uses. Days 11 to 28 walk through real systems the way an interviewer wants them. Three mock interviews show you where you are weak while there is still time to fix it.
How do the mock interviews work?: The AI tutor plays the interviewer. It asks one question at a time, stage by stage: requirements, estimation, API and data model, high-level design, deep dive, reliability and wrap-up. At the end you get a score from 1 to 5 on ten points, each with quotes from your own answers, and three lessons to read next.
What if I miss a day?: Carry on from where you stopped. When you are signed in, this page marks the lessons you finished and shows the next one to read.
How is this different from the free 30-day study plan?: The free plan covers the whole subject by topic. This path is for an interview: it names the exact lessons and guides for each day, and it adds the mock interviews.

This path runs through the System Design course. Here is the whole course, at your price.

The course this path is part of

System Design Masterclass

770 lessons · about 283 hours · 18 free to read

$49 once, lifetime access · pay with PayPal

Get System Design · $49 Read 18 lessons free first

Also from me

AI Engineering

204 lessons · about 211 hours · 10 free to read

$49 once, lifetime access · pay with PayPal

Get AI Engineering · $49 Read 10 lessons free first

Either course includes the AI tutor beside every lesson, 10 questions a day, and the full seven-stage mock interview. Try a mock interview

Other paths

System Design Foundations Senior/Staff Depth AI Engineer Foundations Production Agents

The plan, day by day

The numbers

Scaling

Getting traffic in

Caching

Choosing a database

Spreading data out

Queues

APIs that hold up

Consistency

Edges and the framework

System 1: URL shortener

System 2: rate limiter

System 3: chat

Mock interview 1

System 4: news feed

System 5: notifications

System 6: video

System 7: ride matching

System 8: file sync

When things fail

Mock interview 2

System 9: search box

System 10: payments

System 11: web crawler

System 12: ticket booking

Seeing inside a system

Leaders and lag

Mock interview 3

Fix your weakest points

The company you are interviewing at

Questions about this path

This path runs through the System Design course. Here is the whole course, at your price.

System Design Masterclass

AI Engineering

Other paths

The plan, day by day

The numbers

Scaling

Getting traffic in

Caching

Choosing a database

Spreading data out

Queues

APIs that hold up

Consistency

Edges and the framework

System 1: URL shortener

System 2: rate limiter

System 3: chat

Mock interview 1

System 4: news feed

System 5: notifications

System 6: video

System 7: ride matching

System 8: file sync

When things fail

Mock interview 2

System 9: search box

System 10: payments

System 11: web crawler

System 12: ticket booking

Seeing inside a system

Leaders and lag

Mock interview 3

Fix your weakest points

The company you are interviewing at

Questions about this path

This path runs through the System Design course. Here is the whole course, at your price.

System Design Masterclass

AI Engineering

Other paths