If you've started preparing for software engineering interviews recently, you've probably noticed something interesting. Coding interviews are still important, but they're no longer the whole story. More companies now include a dedicated Object-Oriented Design (OOD) or Low-Level Design (LLD) interview to evaluate how you think about software architecture beyond writing algorithms.
When I first prepared for these interviews, I made the same mistake many developers do. I focused almost entirely on LeetCode, believing that if I could solve enough dynamic programming and graph problems, I would be ready for anything.
Then came my first OOD interview.
Instead of asking me to reverse a linked list or optimize a search algorithm, the interviewer said, "Design a parking lot management system."
I knew what a parking lot looked like, but translating that into classes, relationships, inheritance, composition, interfaces, and design patterns was an entirely different challenge.
That experience completely changed how I approached interview preparation.
Since then, I've gone through dozens of OOD resources while mentoring engineers preparing for interviews at companies like Amazon, Microsoft, Google, and Meta. Some courses are excellent. Others spend hours explaining theory without ever showing you how interviews actually work.
If you're searching for the best Grokking Using OOD Principles course, this guide should save you a lot of time. I compared the most popular options based on what actually matters:
- How well they explain object-oriented thinking
- Whether they prepare you for real interview questions
- The quality of practical design exercises
- Overall learning experience
- Value for your time and money
Here's the list I'd confidently recommend in 2026.
1. Grokking the Low Level Design Interview Using OOD Principles (Educative)
After reviewing dozens of interview preparation resources over the years, this is still the course I recommend first whenever someone asks how to prepare for low-level design interviews.
What impressed me most isn't simply the amount of material. It's the way the course is organized.
Many OOD courses either dive straight into complex interview questions or spend far too much time teaching theoretical concepts without explaining how those concepts appear during interviews. This course strikes a much better balance.
It starts by building your foundation in object-oriented programming. Rather than assuming everyone already understands inheritance, abstraction, polymorphism, and encapsulation, it gradually introduces these ideas before moving into more advanced software design concepts.
From there, the course naturally progresses into SOLID principles, UML diagrams, design patterns, and finally complete low-level system design problems.
That learning progression feels very similar to how experienced software engineers actually grow in their careers. You first understand individual concepts before combining them to solve larger design problems.
One aspect I particularly appreciate is that every design exercise follows a repeatable framework instead of jumping directly to the final solution.
Rather than saying, "Here's the finished class diagram," the instructor walks through questions such as:
- What are the functional requirements?
- What objects exist in this system?
- How should those objects communicate?
- Which design pattern makes sense here?
- How can we make the design extensible?
That thought process is exactly what interviewers are evaluating.
The course also includes over twenty realistic design problems covering systems like parking lots, elevators, hotel management, Amazon shopping, LinkedIn, library management, chess, and car rental systems. These aren't toy examples—they resemble the kinds of problems candidates encounter during actual interviews.
Another feature that sets this course apart is the inclusion of realistic mock interviews. Practicing complete interview scenarios helps bridge the gap between understanding concepts and confidently explaining your design decisions under pressure.
If you're preparing for interviews at companies where low-level system design is part of the hiring process, I genuinely think this is the strongest resource currently available.
Who should take it?
This course is ideal for software engineers preparing for Amazon, Microsoft, Google, Meta, Apple, and similar companies. It's equally valuable if you're moving from frontend development into backend engineering or simply want to become a better software designer.
What I liked
Instead of overwhelming you with isolated concepts, the course builds confidence gradually. By the time you reach the larger interview questions, you've already learned the tools needed to solve them.
Potential drawback
The course requires an Educative subscription, although I personally think the depth of content easily justifies the investment if you're serious about interview preparation.
2. Grokking the Object-Oriented Design Interview (Design Gurus)
Design Gurus has built a strong reputation in the interview preparation space, so it's no surprise that their object-oriented design course appears on many recommendation lists.
The course focuses primarily on preparing candidates for common interview questions rather than teaching software engineering from scratch. If you already have a reasonable understanding of OOP concepts, you'll probably find yourself moving through the material fairly quickly.
I like how the course emphasizes interview-style thinking. You'll encounter familiar design problems such as parking lot systems, movie ticket booking platforms, and online shopping applications.
Where I think it falls slightly behind Educative is the overall depth. While the interview questions are useful, the curriculum isn't quite as comprehensive, and there are fewer opportunities to practice complete end-to-end interview scenarios.
That doesn't make it a bad course—far from it. It's simply a better fit for developers who already have solid programming experience and want additional interview practice rather than a complete learning path.
3. Refactoring Guru
Whenever someone asks me where they should learn design patterns, Refactoring Guru is almost always one of my first recommendations.
Technically, this isn't an interview course. Instead, it's one of the best educational resources available for understanding why design patterns exist and how they solve common software engineering problems.
One thing I really appreciate is how visual the explanations are.
Design patterns can easily become confusing when they're explained using only abstract UML diagrams and textbook definitions. Refactoring Guru uses illustrations, animations, and real-world analogies that make concepts much easier to remember.
If you've ever struggled to understand the difference between Factory, Strategy, Observer, or Decorator patterns, you'll probably enjoy this resource.
That said, it shouldn't be your only interview preparation resource. While it teaches excellent software engineering principles, it doesn't simulate interview discussions or complete low-level design exercises.
I usually recommend pairing it with a dedicated interview course.
4. Low-Level Design Course by Concept & Coding
Not everyone wants to invest in a paid course immediately, and that's perfectly reasonable.
If you're just beginning your low-level design journey, the free YouTube series from Concept & Coding offers a surprisingly solid introduction.
The instructor explains SOLID principles, UML diagrams, object-oriented concepts, and several practical design questions in a very approachable way.
I often recommend these videos to developers who aren't yet sure whether they'll enjoy learning low-level design. Since the content is free, it's an easy way to build your confidence before committing to a larger course.
Of course, free resources have limitations.
The lessons aren't organized into a complete learning path, and there aren't structured exercises or interview simulations that force you to apply what you've learned.
Still, for a free starting point, it's one of the better options available.
5. Object-Oriented Design Courses on Coursera
Coursera offers several university-backed software engineering courses that include object-oriented design topics.
These courses approach software design from an academic perspective rather than an interview preparation perspective.
You'll learn about software architecture, testing strategies, UML, maintainability, and engineering principles that are useful throughout your career.
If your primary goal is becoming a stronger software engineer over the long term, these courses provide excellent theoretical knowledge.
However, if you're interviewing in the next few months, you'll probably need another resource alongside them because most interview-specific questions simply aren't covered in enough depth.
6. Gaurav Sen's Low-Level Design Videos
If you've watched system design content on YouTube, you've almost certainly come across Gaurav Sen.
His teaching style is one of the reasons he's become so popular among software engineers.
Rather than rushing through examples, he takes the time to explain why certain architectural decisions make sense and what trade-offs engineers should consider.
That focus on reasoning is incredibly valuable because interviewers care just as much about your thought process as your final solution.
The only downside is that the videos weren't designed as a structured curriculum. You'll often find yourself jumping between playlists or deciding what to study next.
For self-motivated learners, that's not a major issue.
For beginners who prefer guided learning, a dedicated course may be easier to follow.
7. Head First Design Patterns
Although it's technically a book rather than an online course, I couldn't leave Head First Design Patterns off this list.
Despite being around for years, it remains one of the most approachable introductions to software design patterns ever written.
Instead of presenting dry academic definitions, the authors explain concepts using relatable examples and memorable illustrations.
Even today, many senior engineers still recommend it to junior developers because it teaches principles that remain relevant regardless of programming language or framework.
It's not designed specifically for interviews, but it does provide a strong foundation that makes interview preparation significantly easier.
Which course should you choose?
The truth is that there isn't a perfect course for everyone.
If you're preparing for interviews at companies like Amazon, Microsoft, Google, or Meta, I'd strongly recommend starting with Grokking the Low Level Design Interview Using OOD Principles on Educative.
It provides the most complete learning journey I've seen. You begin with object-oriented fundamentals, gradually learn software design principles, practice design patterns, and eventually solve realistic interview problems that mirror what you'll encounter during hiring loops.
If you already have a strong background in object-oriented programming, Design Gurus is another excellent option for focused interview practice.
If your goal is mastering design patterns rather than interviews, Refactoring Guru and Head First Design Patterns remain outstanding resources that every software engineer should experience at some point.
Final thoughts
One lesson I've learned after years of interviewing and mentoring developers is that low-level design isn't about memorizing class diagrams.
The strongest candidates aren't the ones who remember every design pattern by heart.
They're the engineers who can listen carefully to requirements, identify the right abstractions, explain their reasoning clearly, and design software that's easy to extend and maintain.
That's exactly why I continue recommending Grokking the Low-Level Design Interview Using OOD Principles as the best overall course.
It doesn't just teach you what SOLID principles are or how a Factory pattern works. It helps you develop the design mindset that interviewers actually want to see.
If your goal is to become a stronger software engineer while also improving your chances of clearing modern OOD interviews, it's the resource I'd personally start with.
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