Tutorials System Design Tutorial
HLD vs LLD — Complete Guide
HLD vs LLD — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of System Design Tutorial on Toolliyo Academy.
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System Design Tutorial · Lesson 2 of 100
HLD vs LLD
Basics → Scale → Interview
Basics · 1 — Building blocks · ~6 min · Module 1: System Design Foundations
What is this?
HLD (high-level design) shows major services and data stores. LLD (low-level design) shows classes, APIs, and module internals inside one service.
Why should you care?
Interviews and teams mix them up. ShopNest needs both: a global map and a clear OrderService class design.
See it live — copy this example
Sketch the architecture on paper. These lessons focus on concepts and trade-offs.
HLD: Client → API Gateway → Order Service → Postgres
↘ Inventory Service
LLD (Order Service):
OrderController → CreateOrderUseCase → OrderRepository
DTOs: CreateOrderRequest / OrderResponseRun Example »
This lesson uses terminal or setup steps. Run commands on your computer — the live editor appears on coding lessons.
What happened?
- HLD answers “which services talk?” LLD answers “which classes and methods inside Order Service?” Mixing them creates noisy diagrams.
- Follow the steps below — typing the code yourself is the fastest way to learn.
Practice next
- Write three HLD boxes for ShopNest checkout.
- Pick one box and list 3–5 classes for LLD.
- Label one diagram HLD and one LLD.
- Move Inventory to a separate service on HLD only.
- Add an interface IOrderRepository on the LLD sketch.
Remember
HLD = services and stores. LLD = classes and APIs inside a service. Keep the two diagrams separate.
Design review split
ShopNest architects review HLD; feature teams own LLD PRs.
Outcome: Reviews stay focused and shorter.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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