SevyDevy

Free courseSystem design · Beginner to intermediate · Some coding helps · No system design needed

System Design from ScratchThe system design course for beginners

8 modules · 35 lessons · 7 hours · Free to read · Written lesson by lesson · By Saket Bhatnagar

Researched and drafted with AI, reviewed and edited by Saket Bhatnagar.

In short

System Design from Scratch is a system design course for beginners, in 35 lessons across 8 modules. It follows one ticket-booking app from a single server to millions of users, adding load balancers, caches, databases, queues and reliability one part at a time, each for a reason you can say aloud. Every lesson ends with a question to check yourself.

Lessons
35
Modules
8
Hands-on demos
57
Checks
88
Start the course, freeSee the syllabus

Lala video lessons

Every lesson will also come as a video taught by Lala, your AI mentor, personalized to you. The written lessons are here to read today.

Who it is for

  • Final-year students and freshers who keep hearing “HLD” and “system design” in placement talks and SDE-1 interviews.
  • Working engineers who build features every day but have never designed the whole system behind them.
  • Frontend, mobile, data and QA engineers, and product managers, who want to follow every box in a design review.
  • Career switchers who know a little programming and no backend words at all. No prior system design needed.

What you will be able to do

By the last lesson.

  1. Explain what happens between tapping a button in an app and seeing the result, part by part, in words a friend would follow.
  2. Estimate how many users, requests and how much storage a system needs, and turn those numbers into a first design.
  3. Choose between a cache, a read replica, a shard or a queue for a slow or overloaded system, and say why.
  4. Pick the right kind of database for a feature and explain the trade-off between consistency and availability.
  5. Keep a system running when parts fail, using timeouts, retries, rate limits and monitoring.
  6. Design a real system end to end, such as a ticket-booking app, and present it in a 45-minute interview.

How every lesson works

Built so the idea sticks, not just so you finish.

  1. A story firstEvery idea starts with something from everyday life: a chai stall, an exam, a cricket match.
  2. Then the real ideaThe technical word, explained in plain English, with a diagram that shows how it works.
  3. Try it yourselfPlay with the idea right in your browser, with a small demo built for the lesson.
  4. Check yourselfA short question at the end. Every answer, right or wrong, tells you why.
  5. Watch with LalaA short animated video for every lesson, narrated by Lala. Coming lesson by lesson.

Try one now

This is a real demo from lesson 3.3. Step through it and watch how a load balancer shares requests.

Try it yourselfEight requests, a slow server, a better ruleStep through round robin, a slow server, then least request.

Modules

8 modules and 35 lessons. Read in order, or open any lesson.

  1. Module 1 · 4 lessons · 46 min

    How an App Answers a Tap

    Follow one booking tap from a phone to a server and back: client and server, DNS, HTTP and APIs.

    1. What is system design? Seeing the whole app behind one tap
    2. What is client server architecture? Following one tap there and back
    3. How does DNS work? How a phone finds the right server
    4. What is a REST API? How the app and the server agree on what to say

  2. Module 2 · 3 lessons · 36 min

    Thinking in Numbers First

    Turn a vague idea into requirements, learn latency and throughput, and estimate how much load is coming.

    1. How to define requirements in system design
    2. Latency vs throughput: how fast, and for how many
    3. Capacity estimation in system design: numbers before boxes

  3. Module 3 · 6 lessons · 71 min

    Serving More People, Faster

    Go past one server: scale up or out, make servers stateless, add a load balancer, then cache with Redis and a CDN.

    1. Vertical vs horizontal scaling: a bigger machine or more machines
    2. Stateless vs stateful architecture: where your data waits between taps
    3. What is a load balancer? Sharing requests across servers
    4. How does caching work? Keeping a copy close by
    5. What is Redis used for? A fast shared memory for many servers
    6. What is a CDN? Serving files from a city near the user

  4. Module 4 · 6 lessons · 75 min

    Storing Data That Keeps Growing

    Keep bookings safe with transactions, find them fast with indexes, choose SQL or NoSQL, then copy and split the data.

    1. What is ACID in DBMS? Why a booking is all or nothing
    2. What is indexing in DBMS? Finding one row in ten lakh
    3. SQL vs NoSQL for beginners: picking the right kind of database
    4. What is a read replica? Copies that take the reading load
    5. What is database sharding? Splitting data across machines
    6. How does consistent hashing work? Adding a machine without moving everything

  5. Module 5 · 3 lessons · 38 min

    When Copies Disagree

    Stop double booking, learn what “eventually consistent” really promises, and decide what to do when data centres cannot talk.

    1. How to prevent double booking: two people, one seat
    2. What is eventual consistency? When "late" is not "wrong"
    3. What is CAP theorem? Choosing what to do when the line is cut

  6. Module 6 · 3 lessons · 35 min

    Doing Work Later, Safely

    Move slow work into queues, broadcast events with pub/sub, and make every retry harmless with idempotency.

    1. What is a message queue? Doing slow work later
    2. What is pub sub? One event, many listeners
    3. What does idempotent mean? Making retries safe

  7. Module 7 · 6 lessons · 73 min

    Keeping It Running and Safe

    Survive slow parts and floods of traffic, count nines, set SLOs, see inside the system, and control who may do what.

    1. How to handle failures in distributed systems: timeouts, retries and breakers
    2. What is rate limiting? Saying "slow down" before the system falls
    3. What is high availability? Counting nines and removing single points of failure
    4. SLI vs SLO vs SLA: promising reliability you can measure
    5. What is observability? Seeing inside a running system
    6. Authentication vs authorization: who you are and what you may do

  8. Module 8 · 4 lessons · 54 min

    From One Server to Millions

    Decide when to split into services, replay the whole growth story, practise interview questions, and design your own system.

    1. When to use microservices, and when one app is better
    2. How to scale an app to millions of users, step by step
    3. System design interview questions for freshers, with answers
    4. Capstone: system design projects for your resume

Why this course

An honest look at the usual ways to learn it.

How System Design from Scratch compares with the usual ways to learn system design
Way to learnPricePlain languageHands-on in the browserCheck after every lessonOne growing projectVideo lessonsCertificate
System Design from ScratchPaid, priced for IndiaYes, everyday examples firstYes, a demo in every lessonYes, with a reason for every answerYes, one app grows lesson by lessonComing, narrated by LalaComing, with a final check
Big-brand MOOC coursesSubscription, certificate paidMostlyRarelyQuiz per themeNoYesPaid
Indian live cohorts and bootcamps₹20,000 to ₹3,50,000Often assumes experienceProjects outside lessonsAssignmentsSometimesLive classesYes
Video marketplace coursesAbout ₹1,000 to ₹8,000Varies by teacherCode-along videosOften noneSeparate case studiesYesCompletion only
Interactive text coursesDollar subscriptionAssumes the basicsSomeYesSeparate case studiesFewYes
YouTube playlistsFreeVariesNoNoNoYesNo
Free primers and booksFree or one book priceDense referenceNoNoNoNoNo

Typical prices and features as of October 2026; individual courses vary. Video lessons and a certificate are coming for this course.

Questions people ask about this course

Questions people ask

Do I need to know coding to learn system design?
No. Every lesson starts with an everyday picture and a demo you can tap through. A few optional engineer sections show short code or commands, and you can skip them and still follow the whole course.
Is this course enough for an HLD interview?
It gives you the parts, the numbers and a repeatable way to reason out loud, which is what an HLD round tests. The last module has interview questions with answers and a capstone you present in five minutes. Practise with mock interviews afterwards.
How long does the course take?
About seven hours in total. There are 35 lessons of 10 to 15 minutes each, so one lesson a day finishes the course in about five weeks, or a weekend each for two modules.
Is system design asked in fresher interviews?
It depends on the company. Some product companies ask basic HLD or LLD questions of freshers, and many ask it from SDE-2 upwards. Knowing the basics also helps you follow design discussions in your first job.
What is the difference between HLD and LLD?
HLD, high level design, is the boxes and arrows: servers, databases, caches and queues, and the trade-offs between them. LLD, low level design, is the classes and code inside one box. This course is HLD-first.
Will there be videos and a certificate?
Yes, both are planned. Lala, SevyDevy’s AI mentor, will narrate a short video for every lesson, and a certificate will come with a final check. The written lessons, demos and checks are ready first.

Lesson 1.1 · 10 minutes

Start with “What is system design? Seeing the whole app behind one tap”

Free, no account, no card. Open it and start reading.

Start lesson 1