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Ruby Developer Interview Questions

Position Summary

Ruby developers utilize Ruby to develop back-end components of a web application utilizing the model-view-controller framework. This can include anything from designing plug-ins to building command-line utilities on a computer. Ruby developers are also responsible for supporting front-end developers by integrating third-party web services into applications. 

Ruby on Rails is quickly gaining popularity, creating a demand for Ruby developers. Although Ruby contains properties found in many general-purpose programming languages, a solid understanding of Ruby syntax and common libraries within Ruby such as RSpec and Resque is required to effectively utilize the code.


Ruby developer responsibilities may include:

  • Building data processing scripts
  • Maintaining code integrity
  • Automating processes within the application
  • Designing command-line utilities
  • Designing scalable applications


Ruby is quickly becoming a popular programming language due to its easy-to-learn framework. In order to utilize Ruby to create the best products possible, a skilled Ruby developer will:

  • Possess an eye for detail in order to spot errors in code
  • Possess general knowledge of common programming fundamentals
  • Be committed to delivering the highest quality product possible
  • Think spatially in order to design effective applications
  • Familiarize themselves with the Ruby framework


Entry-level positions typically prefer that candidates have a bachelor’s degree in computer science or a related field. Employers will tend to look for candidates with experience in full-stack web development as well as other common programming languages such as Java and CSS.

If you’re getting ready to interview for a position as a Ruby developer, you can prepare by researching the company as much as possible. Learn about the 9 things you should research before an interview.


Salaries for Ruby developers range between $74K and $120K with the median being $96K. 

Factors impacting the salary you receive as a Ruby developer include:

  • Degrees (associate's or an equivalent certificate, bachelor's, BSc, master's, MSc)
  • Years of Experience
  • Location
  • Reporting Structure (seniority of the manager you report to, number of direct reports, such as junior developers or technicians)
  • Level of Performance - exceeding expectations

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Ruby Developer Interview Questions

Question: Can you explain some advantages of using Ruby to write an application?

Explanation: This is an example of an opening or general question. An interviewer will ask this type of question early in the interview to get you talking, learn more about your background, and gather information they can use for additional questions

Example: “I prefer to code with Ruby because it is a pure object-oriented language. What this means is everything within Ruby is an object, including methods, classes, and booleans. This makes coding much simpler. The other thing I like about Ruby is that it’s 100% open-sourced, so it’s being improved continuously. There’s also a large collection of libraries available.”

Question: Many people describe Ruby as a flexible language. Do you agree with this?

Explanation: This is another general question in which the interviewer is trying to learn a little bit more about your background. There is no right or wrong answer to this question, but it will give the interviewer some perspective as to why you are applying for a job as a Ruby developer.

Example: “Yes, I agree that Ruby is a very flexible language. This is because it allows programmers to alter the elements within the code.  Parts of the lineage can be removed or redefined without any restrictions. An example of this is adding two numbers. Ruby allows you to use the + sign or the word plus.”

Question: Can you list some features of Ruby that you like?

Explanation: By asking this question, the interviewer is testing your knowledge of Ruby. Your answer will indicate the features you use. You should include the most advanced features with which you are familiar. You should also prepare for follow-up questions when you provide your answer.

Example: “Ruby is a feature-rich programming language. I’ve already mentioned that it is object-oriented and flexible; other key features include dynamic and duck typing, a garbage collector to remove unwanted code, and keyword arguments.”

Question: What does freezing an object mean in Ruby, and how would you do this? 

Explanation: This is a technical question which the interviewer will ask to begin testing your skills in Ruby programming. As a programmer, you can anticipate that the majority of the interview will be technical questions. The best way to prepare for these questions is to review the job posting. The employer is likely to list the specific requirements they are looking for.

Example: “Freezing an object in Ruby means to prevent the object from being changed. You can accomplish this using the freeze method which is merely adding the code .freeze after the object’s name.”

Question:  Please list the variables Ruby uses and provide a brief definition for each of them.

Explanation: This is another technical question. The best way to respond to technical questions is directly and concisely. The interviewer will ask follow-up questions if they need additional information.

Example: “There are four different types of variables within Ruby. The first of our global variables begin with the dollar sign and are accessible from anywhere within a Ruby program. The next type is local variables. The scope of a local variable is limited to the code construct within which it is declared. Class variables are shared by all instances of the class in which they are defined. Finally, instance variables begin with @ and are similar to class variables except they are local to a single class in which they are defined.”

Question: Can you explain how thread pooling relates to the thread lifecycle in Ruby?

Explanation: By now, you should recognize this as a technical question. In addition to reviewing the job description, you should also brush up on your Ruby commands, syntax, and structure. This will prepare you to answer specific technical questions the interviewer is likely to ask.

Example: “As you may know, the lifecycle of a single thread begins as soon as computing resources become available. Threads use a lot of resources within a Ruby program, but using multiple simultaneous threads improves the performance of an application. Thread pooling involves using multiple reusable threads. These are created and then stored until the program calls them. This minimizes much of the overhead required by threads. Thread pooling works best when the program as a large number of small tasks.”

Question: Can you discuss how Ruby looks up a method it needs to invoke?

Explanation: This is yet another technical question. As the interview progresses, the questions will become more specific and more difficult. This indicates the interviewer is becoming more confident in your skills and abilities and is willing to explore more complex topics.

Example: “Ruby first looks for a method in the object’s class that contains methods directly defined on the object, known as the metaclass. If the method cannot be found in an object’s metaclass, Ruby will then search for the method in the forerunners of an object’s class. Programmers can also invoke a method missing command to prevent Ruby from continuing to search for the method.”

Question: Please discuss the roles of modules and mixins and how they are used in Ruby.

Explanation: The interviewer is continuing to probe your knowledge of Ruby programming by asking about specific components of the language. If you researched the company and the products they produce before the interview, you’ll be prepared for these types of questions. You may also want to conduct informational interviews with some of the company’s other programmers to learn more about the type of coding they do. These are informal conversations you have with people who may be your peers in the organization.

Example: “Ruby uses modules to group methods, classes, and constants. The program then provides a namespace that will prevent clashes between different names. Mixins enable the modules to share code between different classes. This allows programmers to continue to use the single inheritance paradigm feature within Ruby.”

Question: Can you discuss what unit testing is and describe what you are trying to accomplish when writing a test?

Explanation: As a qualified candidate for this position, you should be comfortable with test or behavior-driven development. The interviewer is continuing to ask specific technical questions. Keep in mind that any response to a technical question may result in a follow-up question which is why it’s best to keep your answers brief and to the point.

Example: “Unit testing is used to verify methods which are the smallest unit in Ruby programming. This enables a developer to clean up an API before other routines consume it within the application. It also verifies the actual result of the method matches an expected result.”

Question: What is RubyGems?

Explanation: This is another technical question asking for a definition of a specific component of Ruby.

Example: “Gems is the name for libraries within Ruby. RubyGems is a package manager software for Ruby libraries. This package manager addresses basic operations and dependency trees and supports asynchronous communication between multiple Gem servers. It is an essential tool used by Ruby programmers to simplify the code and save time.”

Additional Ruby Developer Interview Questions

  • Name some operators used in Ruby.

  • Name the three levels of access control within Ruby.

  • What are blocks and procs?

  • How would you make a large data set displayed on one page more efficient?

  • Can you give me an example of a time you fixed a performance issue?

A word of warning when using question lists.

Question lists offer a convenient way to start practicing for your interview. Unfortunately, they do little to recreate actual interview pressure. In a real interview you’ll never know what’s coming, and that’s what makes interviews so stressful.

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