8 most-asked system design interview questions (+ answers)

Below is a list of 59 confirmed system design interview questions that were asked at Google, Amazon, Facebook, or Microsoft.

We identified these questions by analyzing a dataset of over 300 Glassdoor interview reports that were posted by software engineers, engineering managers, and technical program managers.

And the first thing you’ll want to know is which of these questions are the most common.

Let’s get started.

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System design interview questions

The 8 questions below were the most common out of over 350 system design interview questions that we collected, and they’re listed roughly in order of frequency below (note: we’ve just made minor edits to the phrasing).

Let’s dig into these:

1. How would you design a social media app?

For this question you’ll typically be asked to design a specific app, such as Twitter, Instagram, etc. For this example, we’ll assume the interviewer asked you to design Twitter. Here are some considerations for answering this question:

Ask clarifying questions

Is the interviewer looking for a design of the core features, or a high-level overview of the whole service?
What are the constraints of the system?
What are your assumptions? (traffic distribution, number of active users and tweets, read vs write-heavy)

Design high-level

Back-of-the-envelope calculations: average KBs per tweet, size of new tweet content per month, read requests and tweets per second, etc.
High-level components: write, read, and search APIs; types of databases; SQL vs NoSQL; etc

Drill down on your design

Potential bottlenecks: adding a load balancer with multiple web servers, scalability issues, fanout service slowing down tweets and @replies, etc.
Components that you could dive into: how a user views the home timeline or posts a tweet, the intricacies of the database design, etc.

Bring it all together

Consider: does the final design address the bottlenecks you’ve identified? Does it meet the goals you discussed at the beginning of the interview? Do you have any questions for the interviewer?

For a full answer to this question, take a look at the video guide below from Success In Tech or this text guide from donnemartin on GitHub.

2. How would you design X game?

Another topic that comes up frequently is designing a classic game. The exact game you’ll be asked about varies, but here are some of the most common ones we’ve seen:

Tic-tac-toe
Chess
Boggle
Minesweeper
Cards/poker

Let’s walk through an example of what you could consider, if you were asked to design a Chess game.

Ask clarifying questions

What are the rules of the game?
How many players are there? Are there spectators?
Do we need a timer? Are any other special functions required?

Design high-level

Possible classes for the game: board, piece, spot, etc.
Methods that will be required for things like moving pieces

Drill down on your design

Identify important attributes for each class, such as the grid coordinates and color of each spot
Define how the game will prevent illegal moves and recognize a victory

Bring it all together

Sense check your design, and confirm whether it has met all of the requirements you identified at the beginning of the interview

Some of the above considerations were inspired by this in-depth solution to the question, so feel free to check out that resource.

3. How would you design a parking lot?

For questions like these, interviewers are testing your skills in object-oriented design, to see whether you can apply technical thinking to physical objects.

Ask clarifying questions

Is this a multiple floor parking garage or a single level parking lot?
How many entry and exit points will be needed, and for what types of vehicles?
Are there monetary goals for this parking lot?

Design high-level

Possible use cases: customers parking and paying for their spot, admin managing the system, parking attendants maintaining the lot and helping customers, etc.
Possible classes of the system: ParkingLot, ParkingFloor, Account, ParkingTicket, Vehicle, etc.

Drill down on your design

How will you diagram specific activities? (e.g. customers paying for parking tickets, display panels showing available spots, etc.)
What are the required enums, data types, and constants of the eventual code for the parking lot system?

Bring it all together

Will this system meet the requirements you’ve laid out with the interviewer in the beginning of the session?

For a full answer to this question, take a look at this text guide from Educative.io. You may also find this video walk-through from Think Software useful:

Another typical example of a question that requires you to bring design a technical system that interacts with the physical world is “Design a library management system”.

Watch a former Senior SWE at Meta give a superb answer to this question in the video below:

4. How would you design TinyURL?

URL shortening services like TinyURL provide short link aliases that redirect to longer URLs. Here are some points of consideration to help you work out how to build this kind of system.

Ask clarifying questions

Will users be able to customize the URL?
How long do the URLs last before they expire?
What are the availability and latency requirements for this system?

Design high-level

Back-of-the-envelope calculations: estimate the traffic and storage needs per month, as well as bandwidth and memory requirements
Define the APIs (SOAP, REST, etc) as well as a general database schema (URL mappings and user data)

Drill down on your design

Consider tradeoffs: encoding actual URLs may turn out the same shortened URL for two different users who enter the same URL. System may not work for URLs with URL-encoding. Concurrency may cause problems, etc.
Where will you place load balancers, and how will you cache URLs?

Bring it all together

Is the system you’ve designed highly available, so that URLs will not break if the servers go down? Does it meet any potential business objectives laid out at the start of the interview?

For a full answer to this question, take a look at this text guide from Educative.io.

5. How would you design a web cache?

A distributed web cache is key to many systems, so that the RAM of multiple machines can be accessed in a single in-memory store quickly and reliably. Let’s look at some general points that should help you build out a design.

Ask clarifying questions

Consider the functional and non-functional requirements: put (storing objects under a unique key), get (retrieving objects), scalability, availability, performance, etc.
Specify your assumptions: can we assume that put and get are strings?

Design high-level

Possible data structures for storing data: hash table, queues, doubly linked list
Consider different options to distribute the cache, as well as the benefits of each (e.g. dedicated cache clusters vs co-located caches)

Drill down on your design

Identify the tradeoffs of your choices: Maximum hash table size will prevent from adding more elements, shards may become “hot” (aka process more requests than others), etc.
Data replication could help with “hot” shard bottleneck

Bring it all together

Is the system you’ve designed fast, highly scalable, and available?

For a full answer to this question, take a look at the video guide below from System Design Interview.

6. How would you design autocomplete for a search engine?

If you’ve ever started typing something into a search engine, then you will have seen the suggested “autocomplete” options that are provided. This is also an interesting, and common, system design interview topic. Here are some points you could consider here:

Ask clafying questions

What are the key features? (fast response time, high relevance, number of results, etc.)
What are the functional and non-functional requirements?

Design high-level

What data structure will you use to find suffixes and word completion, and how will you sort the solutions?
How will you store this data structure and connect it with the rest of the system? (Redis cache, database, hash table, API server, load balancer, etc.)

Drill down on your design

How would you modify the frequency of the system without compromising availability or increasing latency?
Consider the fault tolerance of the system – How would you store the already built trie data structure so that in case of failure the system can be restored?

Bring it all together

Is there any more optimization that you could do? Does the system meet the requirements laid out in the beginning of the interview?

For a full answer to this question, take a look at the video guide below from Narendra L.

7. How would you design an API?

APIs are kind of like the bridges that connect the roads of major software products. As a result, they are a central part of the system design of major apps like Instagram, YouTube, Twitter, etc.

Let’s say you were asked, very broadly, to design an API for a website. Here are some examples of how you could go about this:

Ask clarifying questions

Who/what will be using the API?
What is the purpose of the API?
What kind of information does the API need to pass?

Design high-level

Define how the API will be accessed by users (e.g. through a mobile app, website, etc.)
Consider the provider side of the API and the services/databases that will be accessible

Drill down on your design

Should an API gateway be used to improve security?
Will there be an authentication process to access the API?
Will you use a REST API or something different?

Bring it all together

Does your API meet all of the original requirements? Are there any additional considerations, or areas that could use further refinement?

To learn more about API design, check out this mock interview from Exponent, on designing the Twitter API:

8. How would you design a messaging app?

Real-time messaging apps are a common standalone product, or a built-in feature of larger systems. For this question, you might be asked to design a specific app, like WhatsApp or Facebook Messenger.

Ask clarifying questions

What is the scale and profile of the user base?
What features should be incorporated into the messenger? (e.g. text, video, audio, read receipts, message encryption, etc.)
Should we focus on monetizing the system?

Design high-level

How many servers will this system need, and how will clients connect to them?
How will the senders and receivers of messages connect to the servers and database?
Where will the messages be stored, and for how long?

Drill down on your design

How will you scale the system, and where are the bottlenecks?
Deep dive into a component: sent, delivered, read notifications; push notifications; media sharing; database design; etc.

Bring it all together

Have you met the initial goals you and the interviewer laid out for the system?

To see another example of how to answer this question, watch this ex-Google engineering manager answer “Design Telegram”:

How to prepare for system design interviews

As you can see from the complex questions above, there is a lot of ground to cover when it comes to system design interview preparation. So it’s best to take a systematic approach to make the most of your practice time.

Below, you’ll find three preparation steps with links to free resources. You can also refer to our system design interview prep guide and our list of 19 system design interview tips from ex-interviewers.

Alternatively, if you’re looking to save time and access everything you need in one place, we recommend taking The System Design Strong Hire Course. The course includes detailed lessons on system design fundamentals and how to answer system design interview questions, plus mock interview videos with FAANG ex-interviewers (including Google) and more than 100 practice questions.

Otherwise, let’s start with preparation step 1.

1. Learn the concepts

There is a base level of knowledge required to be able to speak intelligently about system design. You don’t need to know EVERYTHING about sharding, load balancing, queues, etc.

However, you will need to understand the high-level function of typical system components. You’ll also want to know how these components relate to each other, and any relevant industry standards or major tradeoffs.

To help you get the foundational knowledge you need, we’ve put together a series of 9 system design concept guides. Here’s the full list:

Network protocols and proxies

, which make it possible for any networked computers to talk to each other, no matter where they are or what hardware or software they’re running.
Databases

, integral components of the world’s biggest technology systems.
Latency, throughput, and availability

, three common metrics for measuring system performance.
Load balancing

, the process of distributing tasks over a set of computing nodes to improve the performance and reliability of the system.
Leader election algorithms

, which describe how a cluster of nodes without a leader can communicate with each other to choose exactly one of themselves to become the leader.
Caching

, a technique that stores copies of frequently used application data in a layer of smaller, faster memory in order to compute costs and to improve data retrieval times and throughput.
Sharding

, the horizontal scaling of a database system that is accomplished by breaking the database up into smaller “shards,” which are separate database servers that all contain a subset of the overall dataset.
Polling, SSE, and WebSockets

, techniques for streaming high volumes of data to or from a server.

We’d encourage you to begin by studying these topics, and once you understand the basics, you can begin practicing system design questions.

2. Work through system design interview questions

As you likely noticed in the common questions section, we recommend using a repeatable answer framework when answering system design interview questions. You can learn more about that framework here, but in the meantime, here is a summary:

Ask clarifying questions

First, spend about five minutes checking in with your interviewer about the functional and non-functional requirements of what you’re going to design. Ask about the system’s goals and how they will be measured. Be sure that you fully understand the question before moving forward.

Call out any assumptions you’re making that will influence your design approach. If applicable, ask about non-functional requirements such as availability, consistency, scalability, etc.

Design high-level

Start the high-level design by specifying one to two metrics (e.g. number of users added, products sold before vs after a feature launch, etc.). Then use these metrics to do some simple calculations in order to find the optimal usage pool of the system.

Once you’ve defined your metrics, map out only the most functional components of the system (e.g. front end, web server, database, etc.).

Finally, before getting into the more detailed aspects of your system, make some decisions on how you will design its database. Choose whether it will be a relational or a no-SQL database, as well as its metadata and table structure.

Drill down on your design

If you haven’t already, start mapping out the system on your whiteboard. Talk through your diagram so that your interviewer is able to follow along and ask questions when necessary.

Consider any bottlenecks that may arise when it comes to the system’s scalability, performance, or flexibility.

To finalize your design, play to your strengths by choosing a component you’re more familiar with and drilling down on it. If you’re not sure which component would be best to explore, ask your interviewer.

Bring it all together

Before wrapping up the round, take about five minutes to re-examine what you’ve designed. Does it meet the objectives you laid out with the interviewer at the beginning of the session? It is okay to change some components at this stage if you think it will improve the system, but you must explain to the interviewer what you are doing and why.

Apply this framework to practice questions like those we’ve included in this article. Use it on different types of questions in a variety of subjects, so that you learn how to adapt it to different situations and respond to unpredictable questions on the fly.

3. Practice with mock interviews

The first step is always to practice by yourself, as we touched on above. Once you’ve got the framework down, start interviewing yourself out loud as you practice. Play both the role of the interviewer and the candidate, asking and answering questions. This will help you develop your communication skills and your process for breaking down problems.

Practice with someone else

Once you’ve done some individual practice, we would also strongly recommend that you practice solving system design questions with someone else interviewing you.

A great place to start is to practice with friends or family if you can. This can help you get some preliminary feedback on your approach, which will be especially helpful if your partner is familiar with system design interviews.

Practice with ex-interviewers

Finally, you should also try to practice system design mock interviews with expert ex-interviewers, as they’ll be able to give you much more accurate feedback than friends and peers.

If you know someone who has experience running interviews at Google, Meta or another big tech company, then that’s fantastic. But for most of us, it’s tough to find the right connections to make this happen.

Here’s the good news. We’ve already made the connections for you. We’ve created a coaching service where you can practice system design interviews 1-on-1 with ex-interviewers from leading tech companies. Learn more and start scheduling sessions today.

System design interview questions

1. How would you design a social media app?

2. How would you design X game?

3. How would you design a parking lot?

4. How would you design TinyURL?

5. How would you design a web cache?

6. How would you design autocomplete for a search engine?

7. How would you design an API?

8. How would you design a messaging app?

More system design interview questions

Google system design interview questions

Facebook / Meta system design interview questions

Amazon system design interview questions

Microsoft system design interview questions

How to prepare for system design interviews

1. Learn the concepts

2. Work through system design interview questions

Ask clarifying questions

Design high-level

Drill down on your design

Bring it all together

3. Practice with mock interviews

Practice with someone else

Practice with ex-interviewers