10 RESTful API design Interview Questions and Answers for api engineers

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1. Can you explain your experience with designing RESTful APIs?

One of the most notable projects I worked on was the redesign of the RESTful API for a large e-commerce platform. The existing API was causing significant performance issues and customer complaints. After researching the problem, I proposed a new RESTful API design that would be more efficient and scalable while also improving the overall user experience.

  1. I started by identifying the key API endpoints based on user feedback and usage data.
  2. Then, I worked on defining the requests and responses for each endpoint, making sure they were clear and consistent.
  3. I also implemented features such as caching and pagination to improve performance.
  4. To ensure the security of the API, I implemented various security measures such as token-based authorization and rate limiting.
  5. To facilitate easy consumption of the API, I provided extensive API documentation, including clearly defined endpoints and sample code snippets.

After implementing the new design, we saw an improvement in response times by an average of 30%, a significant drop in customer complaints and an increase in overall customer satisfaction. These results were achieved through leveraging my knowledge and experience in designing RESTful APIs alongside the latest industry best practices, technologies and standards.

2. What principles do you follow when designing RESTful APIs?

Principles for designing RESTful APIs

When designing RESTful APIs, I follow several principles:

  1. Use HTTP methods correctly: Each HTTP method has a specific purpose, and using them correctly will make your API more intuitive and easier to use. For example, use GET to retrieve a resource, POST to create a new resource, PUT to update an existing resource, and DELETE to delete a resource.
  2. Keep URLs simple and consistent: A good URL structure is essential for an API. It should be easy to understand and consistent across all endpoints. Keep it simple, use nouns to represent resources, and avoid using verbs in the URL.
  3. Use resource representations: When designing your API, it's essential to define the resources that you'll be exposing. These resources should be represented in a simple and consistent way, using popular formats such as JSON or XML.
  4. Implement pagination: If your API returns a large number of resources, it's important to add pagination to avoid performance issues. By limiting the number of resources returned at a time, you'll reduce the server load and improve the user experience.
  5. Provide clear error messages: When an error occurs, your API should return a clear and concise error message. This message should include the error code, a short description of the problem, and a suggestion for how to fix it.
  6. Implement caching: Caching can significantly improve the performance of your API, especially for resources that don't change frequently. By setting appropriate cache headers, you can reduce the number of requests to the server and improve the overall user experience.
  7. Use versioning: Versioning allows you to make changes to your API without breaking existing clients. When introducing changes, it's important to provide a new version of your API so that clients can continue to use the old version if necessary.
  8. Document your API: Finally, it's essential to document your API thoroughly. This documentation should include endpoints, parameters, response codes, and examples of how to use the API.

By following these principles, I've been able to design RESTful APIs that are easy to use and understand. For example, in my previous role, I designed an API for a mobile banking application. The API had a simple and consistent URL structure, used resource representations, and provided clear error messages. As a result, the API was intuitive and user-friendly, leading to a 20% increase in user adoption over six months.

3. How do you ensure the security of your RESTful APIs?

Security is a critical factor in the design of RESTful APIs. Here are some measures I take to ensure the security of my APIs:

  1. Authentication and Authorization: I use authentication mechanisms such as OAuth2 protocol and JSON Web Tokens (JWTs) to ensure that only authorized users can access the API resources. Additionally, I use role-based access control to restrict certain actions based on user roles.
  2. Encryption: I use Transport Layer Security (TLS) encryption to secure data transmission between clients and servers. This ensures that sensitive information such as user credentials and data are protected from eavesdropping attacks.
  3. Input Validation: I ensure that all input data is validated and sanitized to prevent injection attacks such as SQL injection and Cross-Site Scripting (XSS) attacks. This involves using a combination of server-side and client-side validation techniques.
  4. Throttling and Rate Limiting: I implement throttling and rate limiting mechanisms to prevent DoS and DDoS attacks. By imposing limits on the amount of traffic that can be processed in a certain time window, I can prevent malicious users from overwhelming the system and disrupting service.
  5. Logging and Monitoring: I regularly monitor API traffic to detect and respond to security breaches in a timely manner. I log all API requests and responses, and use analytics tools to identify suspicious patterns or anomalies that could indicate an attack.

These measures have proven effective in ensuring the security of RESTful APIs I have designed in the past. For example, a recent project I worked on involved designing an API for a financial institution that handled sensitive customer data. After implementing these security measures, we conducted penetration testing and identified no major vulnerabilities. This gave our client confidence in the security of their API and helped them attract more customers.

4. Can you explain the difference between PUT and POST methods in RESTful APIs?

PUT and POST are two common HTTP verbs used in RESTful API design. While they are similar, there are some key differences between the two.

  • PUT: This HTTP method is used to update existing data in the system. When using the PUT method, the entire object is sent to the server, including any fields that were not changed. For example, say we have a user object with fields "name", "email", and "password". If we only want to update the user's email, we would still need to send the entire user object to the server with all three fields, but with the new email field.
  • POST: This HTTP method is used to create new data in the system. When using the POST method, only the data that needs to be created is sent to the server. For example, if we want to create a new user object, we would only need to send the fields "name", "email", and "password", without including any fields that are not relevant.

In terms of performance and efficiency, the POST method is usually faster and more efficient, since it only sends the data that needs to be created. However, the PUT method is more commonly used in scenarios where the entire object needs to be updated, as it ensures that all fields are still present and valid.

Overall, choosing between PUT or POST will depend on the specific use case and requirements of the system. It's important to carefully consider the data being sent and which method is best suited for the task at hand.

5. How do you handle errors and exceptions in your APIs?

Handling errors and exceptions in APIs is critical to ensure the API is reliable and robust. The following are the strategies that I follow:

  1. Use descriptive error messages: It is important to provide details about the error that has occurred, which assists developers in identifying and solving the issue. I use descriptive error messages that detail the issue and provide recommendations for troubleshooting.
  2. Return error codes: Error codes indicate the type of error that has occurred, making it easier for developers to identify the issue without having to parse through the error message each time.
  3. Log errors: I implement error logging within the API, which helps me identify recurring or critical issues. This data can then be used to make informed decisions while improving the API.
  4. Use consistent responses: I respond to errors and exceptions in a consistent format, making it easier for users and developers to consume the API. This can be achieved by using a standard format for error messages and codes or by using a standard error handling library.
  5. Monitor errors: I use monitoring tools to keep track of errors occurring within the API. This helps me identify trends, track down hard-to-find problems, and proactively address any potential problems.
  6. Implement rate limiting: Rate limiting prevents an excessive number of requests from being sent to the API. This can help prevent API overload and potential downtime.

Implementing these strategies has led me to reduce API errors and improve overall API reliability. As an example, in my previous role, I implemented these strategies for an e-commerce API, which led to a 20% reduction in error rates within the first two months.

6. What is your approach to versioning APIs?

Versioning APIs is a critical aspect of designing RESTful APIs. My approach to versioning involves using the URI format to indicate the version of an API in use. This approach is beneficial as it allows for the maintenance of different versions simultaneously, and clients can switch to a different version when they are ready.

  1. Using URI: One of the ways that I approach versioning an API is by incorporating the version number in the URI. For instance, if the first version of the API has the URI "https://api.example.com/v1/", the second version of the API will be "https://api.example.com/v2/." This approach will enable clients to access different versions of the API simultaneously.
  2. Site Documentation: Another element of my approach is creating a detailed documentation that shows end-users how to access the APIs, which API endpoints are available and how to use them. This way, users will be able to understand the differences between the different versions and choose the one that is best suited for their needs.
  3. Implementing Legacy Policies: Implementing legacy policies that define how long previous versions of an API are supported is another part of my approach. This guarantees that users of outdated API versions can still access them until support expires. For example, outdated API versions receive support for a period of 12 months before they are discontinued.
  4. Monitoring Usage Patterns: Monitoring usage patterns is a vital aspect of my approach. By keeping a tab on how often one version is being used while other versions are not, I can determine if a particular version is becoming obsolete. If so, I might recommend retiring that version or encouraging the clients to switch to a different version. This ensures that the system's resources are optimally allocated, and consumers can enjoy more efficient API service delivery.
  5. API Notifications: Lastly, another aspect of my approach involves sending API notifications to clients about updates or changes. This serves as a feedback mechanism that helps clients stay updated about the latest API versions and versions that are being phased out.

Implementing this approach to versioning APIs has been proven effective as it increases flexibility, fosters up-to-date standards and practices, and ensures that users can quickly access the latest versions without technical errors or complications.

7. Can you explain how caching works in RESTful APIs?

How caching works in RESTful APIs:

  1. When a client sends a request to a RESTful API, the server checks if the request is already cached using the request URL as the cache key.
  2. If the request is cached, the server sends the cached response to the client. This eliminates the need to process the request again, making the response time faster.
  3. If the request is not cached, the server processes the request and sends the response to the client.
  4. Depending on the caching headers set by the server, the client may cache the response for a certain amount of time or until a certain event occurs.
  5. If the client sends the same request again before the cached response expires, the cached response is sent from the client's cache, eliminating the need to send the request to the server.
  6. If the cached response expires or the client needs to make a modified request, the client sends the request to the server, and the caching process starts again.

Using caching in RESTful APIs can significantly improve the performance of an application. For example, in a hypothetical e-commerce website, caching product information can reduce the response time and provide a better user experience. Without caching, if a product page receives 1000 requests per second, the server would have to process and generate a response for each request. However, by caching the product information, the server can take the load off and only generate a response for the first request. The cached response is then sent to the remaining 999 requests, reducing the server load and speeding up the response time.

8. How do you ensure the scalability of your APIs?

When designing RESTful APIs, scalability is an essential factor to consider. To ensure scalability, I follow these best practices:

  1. Use caching: Caching is a technique that allows storing commonly used data in memory or disk for faster retrieval. I use caching techniques to avoid repeated processing of data that can slow down the API. For instance, I implemented a caching system in one of my previous projects that reduced API response times by 50%
  2. Horizontal scaling: I use load balancers to distribute traffic across multiple servers to maximize performance and reduce the load on any single server. In one of my previous projects, I designed the API to handle a large number of users concurrently using the horizontal scaling technique
  3. Monitoring and optimization: I monitor my APIs regularly to analyze performance and identify bottlenecks. These bottlenecks may include slow queries or badly written code. I optimize APIs by rewriting the code or upgrading the hardware to improve performance. Through this approach, I optimized one of my APIs that had a response time of 4 seconds to 500ms.
  4. Use asynchronous processing: Asynchronous processing is a technique that allows API processing to occur in the background while returning an immediate response to the user. The background processing can be used for tasks such as sending emails, processing large files or performing calculations. I implemented this technique in one of my previous projects which reduced response time by 80%

By following these practices, I have been able to develop APIs that can handle high volumes of traffic while maintaining high performance

9. What is your experience with API documentation tools?

Throughout my career, I have worked extensively with a variety of API documentation tools including Swagger, API Blueprint, and RAML. In my previous role as a software engineer at XYZ Company, I was responsible for creating and maintaining the API documentation for our flagship product.

  1. One of my major achievements in this role was consolidating our API documentation into a standardized and user-friendly format using Swagger. This allowed our team to easily navigate the documentation and quickly implement API changes without the risk of introducing errors or confusion.
  2. Moreover, I implemented a continuous integration and delivery pipeline using Swagger that automated the process of publishing updated API documentation to our internal developer portal. As a result, we were able to increase our team’s efficiency by reducing unnecessary communication and troubleshooting time.
  3. Additionally, I leveraged API Blueprint to create interactive documentation that allowed developers to test our API endpoints directly from the documentation. This contributed to an overall increase in developer satisfaction, as it allowed for a more seamless integration with our product.

In short, I am comfortable working with a variety of API documentation tools and have a proven track record of implementing them to improve team efficiency and developer satisfaction.

10. Can you discuss your experience with implementing API testing and monitoring?

Throughout my career, I have gained extensive experience with implementing API testing and monitoring. One specific example occurred during my time at XYZ Company. While working on a new API for a client, I designed and executed a comprehensive testing plan that included both manual and automated testing. This approach helped us uncover several critical bugs that would have otherwise been missed if we solely relied on manual testing.

  1. To perform automated testing, I used tools such as Postman and Swagger to write test cases and created a test suite to run them automatically. This process allowed us to quickly validate the API's responses and ensure that it adhered to the RESTful design principles.
  2. For manual testing, I created a test plan with several test cases ranging from basic to complex scenarios. I also created data sets to test the API's handling of different input data. This process helped me to identify the API's limitations and possible edge cases.
  3. To monitor the API's performance, I set up alerts and logs using tools such as New Relic and Splunk. These tools helped me to identify issues such as slow response times and server errors before the client noticed them, which improved our overall response time and client satisfaction.

By implementing these practices, we were able to deliver a high-quality API that was reliable and well-performing for our client. I will bring this same level of attention to detail and quality assurance to any company I work with.


Congratulations on improving your knowledge of RESTful API design and preparing well for interviews. However, the next step is to write an exceptional cover letter that will get you noticed by potential employers. Check out our guide on writing a captivating cover letter for API engineers that will help you stand out from other applicants by visiting our guide on writing a cover letter. You should also create an impressive CV that emphasizes your skills and experience as an API engineer. Use our guide on writing a winning resume for API engineers to create a remarkable CV by visiting our guide on writing a resume. Now that you're well-equipped and ready, head over to our website and view our remote job board for backend developers. Our website has a wide range of remote API engineer positions from top-tier companies that you can apply to. Visit our job board now at https://www.remoterocketship.com/jobs/backend-developer and find that dream remote job!

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