How to Interview a Ruby Developer and What to Look For?

The most challenging part of onboarding new Ruby developers is, without a doubt, the technical interview. No matter how many candidates you’ve seen before or how many questions you’ve asked, it’s a process that never seems to get easier with time.

The process, of interviewing a Ruby developer, can vary wildly from talking to a senior engineer with 20 years of language experience to a recent graduate with 20 months total experience. But the qualities and core skills you’re looking for in both should be largely the same.

High-quality developers, in any language, should have a set of hard and soft skills that show a certain level of experience, knowledge, and due diligence coming into a firm. In ruby development these skills should, at a minimum, include:

• Practical knowledge and experience using Ruby/Rails
• Front-end development knowledge (HTML5, CSS, JS)
• Database experience and knowledge
• Experience with fundamental tools (GIT/SVN, Project management, etc.)
• CI/CD principles

These skills should make up the foundation of what you’d expect an incoming developer to come with. In addition, you should look for experience in previous projects and an opinion on the best frameworks, tools, and technologies for particular development problems.

This guide goes into detail on the skills, experience, and qualities to look for in an incoming Ruby developer, as well as the questions to ask to find out whether your candidate has the expertise you’re looking for to build successful Ruby apps.

Far from a rigid and immovable guide, these questions are a starting point—a way to open the door in a positive way to create a conversation between you and your leading candidates.

Should you still need assistance beyond this guide to build your team of developers, we are here to help. Just tell us what you need. We can do the work for you and connect you with up to 5 companies within 72h that match your need- all for free.

Soft Skill Questions for Ruby Developers

Soft skills don’t build applications or services, but they do build teams. A successful developer is one that is a key member within a wider group, able to communicate difficult problems and contribute towards a larger solution.

For a closer look at another aspect where soft skills come into play, make sure to read our guide on the management of outsourced Ruby on Rails development teams. Important soft skills you will be looking to assess in this stage of hiring will help make the management step go much smoother.

These questions should help the right candidate demonstrate these skills as they’ve used them in the past.

What positive impacts have you made within previous companies or projects?

An opportunity for candidates to talk themselves up a little. A candidate may discuss one particular problem or challenge they solved which had a major impact on the firm, or talk about a more generalised approach they introduced to a company or team. Some good examples may be to encourage wider adoption of good testing practices, CI/CD, improved coding standards, or better communication practices.

What do you think makes a good collaborative team?

A question that should give insight into how well a candidate is likely to work with others. The answer given here may tell you a lot about how a candidate will fit in with the team members already in place. A good answer may start a conversation about your teams and how they may fit into them.

Imagine I know nothing at all about Ruby, explain it to me as concisely as possible.

A candidate’s communication skills can, at times, be as important as their technical skills. This question can be deceptively tricky, but an ideal candidate will know how to discuss the topic at a high level without getting bogged down in the details.

Have you ever implemented a development strategy that later failed? How soon did you adapt? How did you adjust your approach going forward?

Adjusting to mistakes well is more important than aiming never to make them in the first place—an unrealistic goal. A candidate who can identify a previous mistake, re-evaluate their approach, and adjust how they’re tackling a problem is a very valuable asset to have in your team.

Hard Skills to Look For in a Successful Ruby Developer

Generalised technical skills in software development are the single most valuable asset your team can have. They’re the kind of skills that are hard-won, only through previous experience, working with others and, very often, learning by trial and error. A developer with a strong foundational knowledge and years of practical experience, in any language or technology, can most often tackle previously unseen problems in many related fields and languages.

Looking for these skills can make the difference between average developers and high-flying teams working at maximum efficiency.

Can They Use Someone Else’s Code?

Being able to build applications and programs from start to finish is a great skill to have. What sets apart enthusiastic amateurs from professional developers, however, is the ability to contribute value to a much larger team. In real-world app development, it’s rare to have full-scale projects produced by only one engineer.

Being able to read production code from a variety of sources, learn and understand its structure, and go on to adapt and improve on it is a vital part of professional development. Look for and identify these skills in a candidate, and you’ll be more than 60% of the way to finding a strong new team member.

Do the Tools Align?

A great deal of time, effort, and costs can be saved by onboarding a developer with an understanding of the tools used in-house. By finding that ideal developer, you not only “hit the ground running” but reduce the likelihood of introducing errors and issues into the project too.

Lifelong Learning Skills

The software industry is, understandably, constantly changing. Technologies, languages, and supporting tools are in a continual state of flux and development. A large part of the job description of a software developer is keeping up with these changes, adapting to new ways of doing things, and picking up new skills as you go.

Ruby alone updates on an annual basis. A prospective new hire must be on top of these changes and capable of keeping up with new features and requirements.

Practical Coding for Ruby Developers

Without a doubt, the single best assessment you can give to a developer is to find out how they code in practice. The ideal starting point is to look at their public contributions before they come in, but these only get you so far.

Repositories available on Github or similar services will tell you how well a candidate codes, but they won’t tell you about how a candidate solves and communicates a particular set of problems.

To do this, there are two ways of assigning problems to candidates.

Work Sample Test

Assigning a small coding task to be undertaken by candidates is a great way to find out how they respond to particular technical challenges. These should be small, discrete problems that take no more than a couple of hours to complete.

They should have some similarity to the day-to-day challenges of the role you’re hiring for and involve many of the same technologies and, if possible, the same tools.

Such challenges have been shown in the past to be one of the best predictors of real-world job performance.

Advantages:

• They mirror as closely as possible the actual work a candidate will be called on to perform in their job
• An excellent predictor of job success
• Results are easy to compare with other candidates

Drawbacks:

• There are limits to how much work and time a candidate should be expected to provide for free
• The process of hiring and interviewing is already time-consuming and costly. Employers should be conscientious of these factors when selecting candidates to fill a role

Open Source Contribution

Much like the work sample test, an Open Source contribution that you both agree to ahead of time is an excellent way for candidates to show their problem-solving skills and for you to see how they respond to real-world development challenges.

Having candidates choose an open-source contribution to make themselves is an ideal way to let them show their skills in their best light and see how they handle themselves under some real-world pressure. Unlike producing code for a toy example or simple demo, an open-source contribution has the potential to make a real impact and stick around for some time to come.

For the candidate, the advantage of this approach is that it can further their knowledge of a technology they’re interested in and boost their future ambitions in the open-source community.

Evaluating Candidate Solutions

Whichever method you choose, have candidates talk through their code and the solution they’ve developed. Offer up the topic as a point of discussion, ask questions about the work and find out about the challenges they encountered and how they overcame them.

As a real-world exercise, you’ll never get a better chance to see how a candidate performs.

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Ruby Interview Questions

What are the data types available in Ruby?

A question that may be used when testing their fundamentals of the language.

• Numbers
• Strings
• Symbols
• Hashes
• Arrays
• Booleans

What variables are available in Ruby?

• Local—Available only within the construct it’s created
• Class—Available in all instances of the class
• Instance—Available in a single instance of the class
• Global—accessible anywhere

What are Modules in Ruby?

Ruby modules group methods and classes into a single namespace to prevent clashes.

How is load and require used in Ruby?

Load and require both are used for loading the available code into the current code. It’s good practice to use after a change, or the URL is entered. Require is used when autoload is used.

Ruby on Rails Interview Questions

You can’t talk at length about Ruby without also coming to the topic of Ruby on Rails. There will be very few developers who have worked extensively with the former and very little with the latter. Included here are some valuable questions that can give you insight into a candidate’s experience with rails and familiarity with the framework.

What is the difference between Ruby and Ruby on Rails?

Rails is a server-side web application framework written in Ruby. Ruby on Rails provides a framework for developing web applications with Ruby.

What Does Rails add to Ruby?

Showing a candidate knows what values and qualities a framework brings to a project demonstrates a much deeper understanding. A good answer should discuss the advantages of the framework.

• Cutting time to produce web apps
• Convention Over Configuration philosophy

What are alternatives to Ruby on Rails?

Some examples might include:

JavaScript:

• Node.js
• Angular

Python:

• Django
• CherryPy

Any others a candidate may have worked with in the past could be a valid choice.

If you don’t know where to get started familiarizing yourself with available Ruby frameworks, take a look at our guide to Ruby development frameworks in 2021.

What are the advantages of Ruby on Rails?

Ruby on Rails is a highly mature framework. It’s constantly innovating with new features, but the core framework has been relatively stable for some time.

Rails facilitates rapid MVP development with a large number of ‘gems’ and plugins to support the platform.

What Ruby on Rails gems do you know of, and which have you used?

An open-ended question that invites further discussion on previous experience and applications previously produced.

What is DRY code?

DRY stands for Don’t Repeat Yourself. One of the main principles of rails development is generating concise code that doesn’t have to be repeated elsewhere in the codebase.

What are common Rails mistakes that impact page loading times?

• Missing indexes on columns in the database resulting in longer queries execution
• Eager loading leading to too many queries sent to a database
• Having too many gems dependencies negatively affects performance in a big way