Extend Software Engineer Interview Questions + Guide in 2025

Extend is a rapidly growing fintech startup revolutionizing the B2B payments space through innovative virtual card solutions for banks and their customers.

As a Software Engineer at Extend, you will take a leading role in architecting, developing, and scaling the backend platform that powers our unique virtual card offerings. Your responsibilities will include designing scalable and flexible services that align with the company's dynamic growth and technological vision. You will also be instrumental in driving innovation by developing new features that leverage AI and advanced insights to enhance user experience. Your role will involve overseeing integrations with major financial institutions, ensuring data flows are optimized and functionality is enhanced, all while setting high standards for engineering excellence within the team.

To excel in this role, you should have extensive experience in building complex distributed systems, a strong background in software development with a focus on object-oriented design, and proficiency in modern backend technologies, particularly within a cloud environment like AWS. Leadership qualities such as mentoring other engineers and staying ahead of technological trends are also vital to ensuring Extend remains competitive in the fintech sector.

This guide will help you prepare thoroughly for your interview by emphasizing the key skills and experiences that Extend values in its Software Engineers, allowing you to showcase your fit and readiness for this exciting opportunity.

The interview process for a Software Engineer at Extend is designed to assess both technical skills and cultural fit within the company. It typically consists of several stages that evaluate your problem-solving abilities, system design knowledge, and collaborative mindset.

1. Initial Screening

The process begins with an initial screening, which is usually a 30-minute phone interview with a recruiter. This conversation focuses on your background, experiences, and motivations for applying to Extend. The recruiter will also provide insights into the company culture and the role's expectations, ensuring that you understand the environment you may be joining.

2. Technical Assessment

Following the initial screening, candidates typically undergo a technical assessment. This may involve a coding challenge or a take-home assignment that tests your ability to solve real-world problems relevant to the role. The focus here is on your coding skills, particularly in languages and frameworks pertinent to Extend's tech stack, such as Kotlin and Spring Boot. You may also be asked to demonstrate your understanding of system design principles, especially in the context of scalable and flexible architectures.

3. Technical Interview

The next step is a technical interview, which is often conducted via video call. In this round, you will engage with a senior engineer or a technical lead. Expect to discuss your previous projects and experiences in detail, as well as tackle system design questions that reflect the challenges faced at Extend. This interview will assess your ability to architect solutions and your familiarity with cloud services, particularly AWS.

4. Behavioral Interview

After the technical rounds, candidates typically participate in a behavioral interview. This session aims to evaluate your alignment with Extend's values and culture. You will be asked about your teamwork experiences, leadership qualities, and how you handle challenges in a collaborative environment. The goal is to ensure that you not only possess the technical skills but also the interpersonal skills necessary to thrive at Extend.

5. Final Interview

The final interview is often with the CTO or another senior leader within the company. This round is more strategic and focuses on your vision for technology and innovation within the fintech space. You may discuss your thoughts on industry trends, your approach to mentoring other engineers, and how you would contribute to setting engineering standards at Extend.

As you prepare for these interviews, it's essential to be ready for a variety of questions that will test your technical knowledge and problem-solving abilities.

Here are some tips to help you excel in your interview.

Emphasize Problem-Solving Skills

During your interview, focus on demonstrating your ability to solve complex problems through coding and system design. Prepare to discuss specific examples from your past experiences where you successfully tackled challenging engineering issues. Highlight your thought process and the methodologies you employed to arrive at effective solutions. This will resonate well with Extend's emphasis on practical problem-solving over theoretical algorithms.

Showcase Your Technical Expertise

Given the role's requirements, ensure you are well-versed in the technologies and frameworks relevant to the position. Brush up on your knowledge of Kotlin, Spring Boot, and AWS services, as these are critical to the role. Be prepared to discuss your experience with high-scale web applications and distributed systems, as well as your understanding of object-oriented design and multithreading. Demonstrating a strong command of these areas will set you apart as a candidate.

Prepare for System Design Questions

Expect to encounter system design questions that assess your ability to architect scalable and flexible services. Familiarize yourself with common design patterns and best practices in software architecture. Practice articulating your design choices and the trade-offs involved in your decisions. This will not only showcase your technical skills but also your ability to think critically and strategically about engineering challenges.

Align with Company Culture

Extend values a collaborative and innovative culture. Be prepared to discuss how you can contribute to this environment. Share examples of how you have worked effectively in teams, mentored junior engineers, or driven innovation in your previous roles. Show that you are not only a technical fit but also a cultural fit for the company.

Stay Current with Technology Trends

As a Principal Engineer, you are expected to be a tech visionary. Demonstrate your awareness of current technology trends and how they can be applied to enhance Extend's offerings. Discuss any recent advancements in fintech or software engineering that excite you and how you envision leveraging them in your role. This will illustrate your proactive approach to staying ahead in the industry.

Ask Insightful Questions

Prepare thoughtful questions that reflect your interest in the role and the company. Inquire about the engineering team's current challenges, the company's vision for future growth, or how they measure success in engineering initiatives. This not only shows your enthusiasm but also helps you gauge if Extend is the right fit for you.

By following these tips, you will be well-prepared to make a strong impression during your interview at Extend. Good luck!

In this section, we’ll review the various interview questions that might be asked during an interview for a Software Engineer position at Extend. The interview process will focus on your problem-solving abilities, system design skills, and cultural fit within the company. Be prepared to discuss your experience with backend technologies, cloud services, and your approach to software architecture.

System Design

1. Can you design a scalable ordering system for a virtual card platform?

This question assesses your ability to architect a system that can handle high traffic and complex transactions.

How to Answer

Discuss the components of the system, including databases, APIs, and user interfaces. Highlight how you would ensure scalability and reliability.

Example

“I would design the ordering system using microservices architecture, where each service handles a specific function such as order processing, payment processing, and user management. I would use AWS services like RDS for the database and SQS for message queuing to ensure that the system can scale horizontally and handle peak loads efficiently.”

2. How would you approach integrating with a major financial institution?

This question evaluates your understanding of integration challenges and your experience with APIs.

How to Answer

Explain the steps you would take to ensure a smooth integration, including security considerations and data flow management.

Example

“I would start by reviewing the API documentation provided by the financial institution to understand their requirements. Then, I would implement OAuth for secure authentication and set up a robust error handling mechanism to manage any issues during data exchange. Finally, I would conduct thorough testing to ensure that the integration meets all functional and performance criteria.”

3. Describe a time when you had to refactor a legacy system. What was your approach?

This question looks for your experience with improving existing systems.

How to Answer

Discuss the challenges you faced and the strategies you employed to refactor the system while minimizing downtime.

Example

“In my previous role, I was tasked with refactoring a monolithic application into microservices. I started by identifying the most critical components and gradually extracted them into separate services. I ensured that each new service was thoroughly tested before deployment, allowing us to maintain functionality while improving the system's scalability and maintainability.”

4. What strategies would you use to ensure high availability in a distributed system?

This question tests your knowledge of system reliability and fault tolerance.

How to Answer

Discuss redundancy, load balancing, and failover strategies that you would implement.

Example

“To ensure high availability, I would implement load balancing across multiple instances of the application and use a multi-region deployment strategy. Additionally, I would set up health checks and automatic failover mechanisms to redirect traffic in case of an instance failure, ensuring minimal downtime for users.”

Technical Skills

1. What is your experience with AWS services, and how have you utilized them in past projects?

This question assesses your familiarity with cloud technologies.

How to Answer

Provide specific examples of AWS services you have used and how they contributed to the success of your projects.

Example

“I have extensive experience with AWS, particularly with EC2 for hosting applications and RDS for managing databases. In a recent project, I used Lambda functions to process payments asynchronously, which significantly improved the system's responsiveness and reduced costs by only using resources when needed.”

2. Can you explain the differences between SQL and NoSQL databases? When would you choose one over the other?

This question evaluates your understanding of database technologies.

How to Answer

Discuss the characteristics of both types of databases and provide scenarios for their use.

Example

“SQL databases are relational and are best suited for structured data with complex queries, while NoSQL databases are more flexible and can handle unstructured data. I would choose SQL for applications requiring ACID compliance and complex transactions, while NoSQL would be ideal for applications needing scalability and flexibility, such as handling large volumes of user-generated content.”

3. Describe your experience with Kotlin and functional programming. How do you apply these concepts in your work?

This question assesses your programming skills and familiarity with modern languages.

How to Answer

Discuss your experience with Kotlin and how you leverage functional programming principles in your projects.

Example

“I have been using Kotlin for developing backend services, taking advantage of its concise syntax and null safety features. I apply functional programming concepts by using higher-order functions and immutability, which helps in writing cleaner and more maintainable code.”

4. How do you ensure code quality and maintainability in your projects?

This question evaluates your approach to software development best practices.

How to Answer

Discuss your strategies for code reviews, testing, and documentation.

Example

“I ensure code quality by implementing a rigorous code review process where peers provide feedback on each other's work. I also write unit and integration tests to catch issues early and maintain comprehensive documentation to help future developers understand the codebase.”

Cultural Fit

1. How do you approach mentoring junior engineers?

This question assesses your leadership and mentoring skills.

How to Answer

Discuss your philosophy on mentorship and how you support the growth of others.

Example

“I believe in leading by example and providing constructive feedback. I regularly hold one-on-one sessions with junior engineers to discuss their progress and challenges, and I encourage them to take ownership of their projects while providing guidance when needed.”

2. Describe a time when you had to work with a team to solve a complex problem. What was your role?

This question evaluates your teamwork and collaboration skills.

How to Answer

Highlight your contributions to the team and how you facilitated collaboration.

Example

“In a previous project, our team faced a significant performance issue. I organized a brainstorming session where we collectively analyzed the problem and identified bottlenecks. I took the lead in implementing the proposed solutions, which ultimately improved the system's performance by 40%.”

3. What do you think is essential for maintaining a positive team culture?

This question assesses your understanding of team dynamics and culture.

How to Answer

Discuss the importance of communication, respect, and inclusivity in a team environment.

Example

“I believe that open communication and mutual respect are crucial for a positive team culture. I encourage team members to share their ideas and concerns freely, and I make it a point to recognize individual contributions, fostering an environment where everyone feels valued and motivated.”

4. How do you stay updated with the latest technology trends and advancements?

This question evaluates your commitment to continuous learning.

How to Answer

Discuss the resources you use to keep your skills current and how you apply new knowledge.

Example

“I regularly read industry blogs, attend webinars, and participate in online courses to stay updated with the latest trends. I also engage with the developer community through forums and meetups, which helps me learn from others’ experiences and share my insights.”