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How to master Product & API Design Interviews 

We leverage APIs nearly every day as developers, so it's no surprise that API Design Interviews (also called Product Design Interviews) have exploded in popularity.


I first encountered these interviews when I was a candidate at Facebook. Given the choice between a System Design (called "Pirate") or an API/Product Design round (called "Pirate X"), I opted for System Design because of my specialization. However, API Design will make more sense for many engineers — especially in 2024 and beyond. Ace your prep with the software engineer interview cheat sheet and make a fool-proof study plan. 


Today I'll talk about why skimping on API Design Interview prep is no longer an option for software engineers. For instance, at Meta, a strong API Design Interview can mean the difference between starting as an E5 rather than an E4 — an advantage worth tens of thousands of dollars or more in net income.


Then I will offer a few concrete steps you can take to maximize your chances of success in design interviews.


Here’s a high-level summary of what we’ll cover:


  • A quick overview of APIs

  • API Design vs. System Design Interviews

  • A 4-step process for answering API Design questions (REDCAMEL)

  • How to strengthen your API Design skills


Let’s dive in!

A quick overview of APIs (and why they're important)

Put simply, APIs are the interface through which different software components, services, and platforms communicate and share data. 


APIs offer many benefits:


  • Streamlining Development: APIs accelerate development by providing pre-built functionalities, reducing time and costs.

  • More Flexibility: APIs provide a flexible way for developers to access and utilize functionalities of existing services (without reinventing the wheel).

  • Wider Reach: APIs enable businesses to extend their services to a broader audience, including partners, third-party developers, and customers, thus increasing market reach.

  • Facilitating Integration: APIs enable different software systems to communicate and share data with each other effectively.


Ultimately, robust API Design not only influences the efficiency and performance of individual software applications, but also underpins the foundation of interconnected digital ecosystems. At their best, APIs work to drive progress and innovation across many industries.


With all this considered, it's no wonder API design is becoming a staple in modern software development.

API Design vs. System Design Interviews in 2024 

There are many similarities between API and System Design Interviews.


For one, there can be various possible solutions to a given design interview problem. There's rarely a “right” or “wrong” answer. This is a contrast to coding interviews, where the final solution is a huge determinant of your success. These interviews are less interested in candidates' coding abilities, and more interested in their design thinking skills. 


That said, as a candidate, your problem-solving process and decision-making are just as important to your success as the solution you present (and just as important: you should communicate your thinking along the way).


In addition, both API and System Design Interviews are typically used to help determine a candidate’s starting level and salary. The repercussions of stepping into a design interview ill-prepared can be severe — this can potentially lead to being downleveled into a less senior role or, worse, missing out on a crucial career opportunity.


So, given a choice between API and System Design Interviews, which should you pick?


Your choice will largely depend on your career path. 


For System Architects and Cloud Architects (or any candidate working primarily on designing distributed systems at scale), System Design Interviews are an obvious choice. 


While System Design (and its building blocks) remains an essential skill, the majority of software engineers are now tasked with building products upon existing systems. This means we’re often leveraging building blocks of existing systems — not creating them. That’s where APIs most frequently come into play. 


Front-end, back-end, and full-stack web developers will benefit strongly from a working knowledge of API Design. Most developers will use existing APIs to create applications, however, you're likely to have to change APIs or design your own eventually in your career. That said, designing is an essential skill to create any application.


Architects will mostly be involved in creating new APIs; whereas junior or senior developers may be involved in reusing existing APIs and even rebrand certain functionalities through their own set of API endpoints.


While expectations will be different for each, both junior and senior developers can be assessed in API Design Interviews. Making sure your design skills are top-notch means truly understanding the inner and outer workings of the request, and optimizing the whole lifecycle of that request. 

Unpacking API Design Interviews

API Design Interviews consist of several stages. 


The interview typically commences with a broad problem statement, requiring candidates to swiftly grasp and clarify functional and non-functional requirements. 


Transitioning into the design phase, candidates will need to be prepared to delve into any of  the following topics:


  • Architectural Considerations 

  • Endpoint Structuring

  • Data Format Selection


The interview will then assess your ability to interpret and discuss optimization techniques, i.e. how you will optimize your design within a stipulated latency budget. This is where it can be helpful to recall techniques such as client-side rendering and server-side rendering. 


Of course, you have to do this all in a limited time frame of about 40 minutes. To ensure you're able to demonstrate your skills and lead the conversation well, it's important to have a strong grasp of the technical content, and a strategy to stay within scope in the allotted time.

A 4-step process for answering API Design questions (REDCAMEL)

We created the REDCAMEL framework to help you check off all the necessary boxes in API Design Interviews


REDCAMEL is a mnemonic device to help you structure your approach to API design questions. 


  1. Requirements (RE): Clarify requirements by defining both functional and non-functional aspects while articulating the problem statement and rationale behind the API. Additionally, conduct initial estimations concerning data pipelines and expected usage.

  2. Design Considerations (DC): Consider the high-level design of the API. This involves selecting appropriate architecture styles like REST, GraphQL, or gRPC, and determining data formats (e.g., JSON, XML, binary) and communication protocols.

  3. API Model (AM): Develop the API model by establishing a base URL and necessary endpoints, identifying critical data elements, defining request-response formats, and outlining failed request status codes.

  4. Evaluation and Latency Budget (EL): Evaluate design choices, suggesting improvements where needed, and revisit initial calculations to derive proposed response times, ensuring they align with the latency budget.

Remember, interviewers can't read your mind — so be sure to narrate your thought process behind your design choices.

How to strengthen your API Design skills

For many of us, skipping on mastering API design can lead to missing otherwise well-deserved opportunities and potential earnings. 


Whether you're gearing up for an interview or looking to sharpen your API design skills, I do advise developers in any stage of their career to boost their competitiveness by becoming more comfortable with applied API and Product Design.


To help you get hands-on design practice, we created a comprehensive course, Grokking the API Design Interview. Created by industry experts, this course will prepare you with the fundamental concepts and techniques needed to craft API designs.


You'll get hands-on with real-world design problems of various types and difficult levels, including APIs from:

  • YouTube 

  • Stripe

  • Zoom 

  • …and more


And, in case you encounter any unfamiliar problems in the interview, you'll be equipped with  foundational knowledge and the 4-step REDCAMEL framework to move forward.

Commonly Asked API Interview Questions
  1. What is an API?

  2. Explain the difference between API and Web Services.

  3. What are some architectural styles for creating Web API?

  4. What is API testing, and why is it important?

  5. What is CRUD?

  6. Why should we use a Web API?

  7. What are the limitations of API usage?


Explore more API Design interview questions at Educative and build skills you will carry with you in your career for years to come.


I hope you take the opportunity to prioritize the long-term growth of your career and strengthen your API Design skills today.


As always, 


Happy learning!

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