System Design

System Design: The Complete Guide (HLD, LLD & Interview Prep)

Learn system design from scratch to senior level — the complete free guide covering fundamentals, high-level design (HLD), low-level design (LLD), design patterns, and real interview case studies. Beginner-friendly explanations with senior-grade depth.

Shiv Pandey

Sep 22, 2026 | 9 views

System Design: The Complete Guide (HLD, LLD & Interview Prep)

Welcome — this is the page I wish I'd had when I started. Whether you've never heard the term "system design" or you're prepping for a staff-engineer interview, this guide takes you the whole way: from "what even is a server?" to designing systems that serve millions of users and writing clean object-oriented code under interview pressure. Everything is explained in plain English first, with real analogies, and then goes as deep as you want. Bookmark it — you won't need another site.

How to use this guide. Follow it top to bottom like a course, or jump to any topic. Every article is tagged by level so you know what you're getting:

🟢 Fresher — start here, zero background needed · 🔵 Mid · 🟠 Senior · 🔴 Super-senior

Each article itself starts simple and climbs, so a beginner and a senior both get value from the same page.

First, the big picture: HLD vs LLD

System design splits into two halves, and interviews test both:

	HLD — High-Level Design	LLD — Low-Level Design
Question	"Design Instagram for 100M users"	"Design a parking lot in code"
About	Architecture: servers, databases, caches, queues	Classes, objects, design patterns, clean code
You draw	Boxes and arrows (components)	Class diagrams (UML)

New to the difference? Start with HLD vs LLD explained. Then follow the path below.

🟢 Branch 0 — Start Here (never done this before? begin here)

The absolute basics, explained like you're five. No prior knowledge assumed.

What is System Design? — and why every engineer needs it
How the Web Works — what actually happens when you type a URL
Servers, Databases & APIs — the basic building blocks in plain words
Latency, Throughput & Availability — the vocabulary engineers use
Scaling from Zero to Millions of Users — the story that ties it all together

🔵 Branch 1 — Fundamentals (the building blocks)

Every concept you'll reuse in every design. Learn these once, apply them forever.

🟠 Branch 2 — HLD: Design Real Systems

Apply the fundamentals to the exact questions asked at Google, Amazon, and every top company.

Design a URL Shortener (TinyURL) — the perfect first design
Design a Rate Limiter · Design Search Autocomplete
Design a News Feed (Twitter/Facebook) · Design a Chat System (WhatsApp)
Design a Notification System · Design a Web Crawler
Design a Distributed Cache · Design a Key-Value Store (DynamoDB)
Design YouTube · Design Uber
Design a Payment System · Design Dropbox · Design Ticketmaster

🟠 Branch 3 — LLD: Object-Oriented Design & Patterns

The code-level design and "machine coding" rounds — huge for SDE-2 and senior roles. This builds directly on object-oriented programming.

Foundations: How to Approach an LLD Interview · OOD Basics · SOLID Principles · UML Class Diagrams

Design Patterns (start with the patterns overview): Singleton · Factory · Builder · Strategy · Observer · Decorator · Adapter · State · and more.

Machine-coding problems: Parking Lot · Elevator · Vending Machine · BookMyShow · Splitwise · LRU Cache · Tic-Tac-Toe · ATM and more.

📌 Quick references (keep these open during interviews)

System Design Cheat Sheet — every concept on one page
Design Patterns Cheat Sheet
The 6-Week System Design Study Plan

Where to start (my honest advice)

Here's what I tell everyone who asks me how to learn this. Don't try to memorise designs — it never works, and interviewers can tell instantly. Instead, learn the fundamentals deeply (the boring stuff: caching, databases, queues), because every "impossible" design question is just those Lego bricks snapped together in a new shape. Start with the 0-to-millions story if you're new, or the 6-step framework if you have an interview soon. Then do two designs by hand — the URL shortener for HLD and the parking lot for LLD — actually drawing them out, out loud. Do that, and you'll walk into the room reasoning from a model instead of reciting from memory. That's the whole game. Take your time, enjoy it — this stuff is genuinely fun once it clicks.