Castlight Software Engineer interview questions & guide 2026

These questions are based on real interview experiences from candidates who interviewed at this company. You can practice answering them interactively on Dataford to better prepare for your interview.

Preparation for Castlight requires a blend of fundamental computer science knowledge and practical application development skills. The interview team looks for engineers who can not only solve algorithmic problems but also discuss the "why" and "how" behind their architectural choices.

You will be evaluated on the following key criteria:

Technical Proficiency & Fundamentals Your interviewer will assess your grasp of core computer science concepts, specifically Data Structures and Algorithms (DSA). While the difficulty is generally rated as "Medium," you must demonstrate clean coding practices and the ability to optimize for time and space complexity. Recent interviews have also placed significant emphasis on specific frameworks like Spring Boot and Angular, as well as database query writing.

System Design & Architecture For mid-to-senior roles, you will face questions regarding REST API design and system scalability. You need to show that you can design robust backend services that integrate well with frontend applications. Expect to discuss trade-offs, data modeling, and how you structure applications for maintainability.

Communication & Collaboration The Castlight interview style is often described as a "discussion." Interviewers value candidates who can articulate their thought process clearly. You will be evaluated on how you handle feedback, how you clarify ambiguous requirements, and your willingness to engage in a two-way dialogue rather than just delivering a monologue.

Culture Fit & Adaptability Castlight values diversity of thought and a user-first mindset. You will be assessed on your ability to work in a collaborative environment where cross-functional teamwork is essential. Be prepared to discuss past projects in depth, explaining your specific contributions and how you navigated challenges within a team.

The interview process at Castlight is structured to evaluate both your technical depth and your cultural alignment. It typically begins with an initial screening, often with a recruiter, to verify your background and interest. This is followed by one or two technical phone or video screens. These rounds usually involve a mix of coding exercises via a shared editor and conceptual discussions about your past work.

If you pass the screening stage, you will move to the onsite (or virtual panel) loop. This stage is rigorous and can involve 3 to 5 separate rounds. You will meet with potential peers, hiring managers, and cross-functional partners (such as Product Managers). These sessions cover live coding, system design, and behavioral questions. The atmosphere is generally described as welcoming and professional, though the process can be lengthy depending on scheduling.

One distinctive aspect of the Castlight process is the emphasis on "discussion" over interrogation. Interviewers often frame questions as collaborative problems. However, candidates should be prepared for a process that requires patience; timelines can vary, and proactive communication is sometimes necessary to keep things moving.

This timeline illustrates the typical flow from application to offer. Note that the Technical Screen phase may involve multiple rounds (coding focus vs. project focus) before moving to the final panel. Use the time between rounds to review your fundamental concepts and practice explaining your past project decisions.

Based on candidate data, Castlight’s technical evaluation focuses heavily on practical coding skills, framework knowledge, and system design fundamentals.

Data Structures & Algorithms (DSA)

This is a core component of the screening and early onsite rounds. You are expected to write syntactically correct code and optimize your solutions.

Be ready to go over:

• Arrays and Strings – Manipulation, sliding windows, and two-pointer techniques.
• Graphs and Trees – Traversal algorithms (BFS/DFS) are frequently mentioned.
• Logic Puzzles – Game-based logic (e.g., designing a game board or solver) has appeared in past interviews.
• Hash Maps & Sets – Efficient data retrieval and storage.

Example questions or scenarios:

• "Implement the logic for a Minesweeper game, handling board generation and user clicks."
• "Traverse a graph to find the shortest path between two nodes."
• "Solve a medium-level array manipulation problem to find specific target values."

Frameworks & Practical Application

Unlike some companies that focus solely on LeetCode, Castlight often tests your knowledge of the tools you will actually use on the job.

Be ready to go over:

• Spring & Spring Boot – Dependency injection, annotations, and creating microservices.
• REST APIs – Designing endpoints, handling HTTP methods, and status codes.
• Frontend Frameworks – Questions on Angular logic and component lifecycle (for full-stack roles).
• Database Queries – Writing raw SQL queries or discussing ORM mapping.

Example questions or scenarios:

• "How would you design a REST API for a healthcare scheduling system?"
• "Explain the difference between specific Spring annotations and when to use them."
• "Write a SQL query to fetch patient records based on complex join criteria."

Behavioral & Project Experience

You will likely have a specific round dedicated to your past experience and behavioral responses, often with a Hiring Manager.

Be ready to go over:

• Project Deep Dives – Explaining the architecture of a previous project and your specific role in it.
• Conflict Resolution – How you handled a disagreement with a product manager or another engineer.
• Mentorship – How you support junior team members (for senior roles).

The word cloud above highlights the frequency of topics reported by candidates. Notice the prominence of Coding, Design, and Manager discussions. This indicates that while technical skills are the entry gate, your ability to interact with management and discuss high-level design is equally critical for the final decision.

As a Software Engineer at Castlight, your daily work will revolve around building scalable, secure, and user-friendly healthcare solutions.

• Feature Development: You will design and implement new features for the Castlight platform, working across the stack or focusing on backend services depending on your team. This involves writing clean, testable code in languages like Java.
• API Design & Integration: You will build and maintain robust RESTful APIs that serve as the backbone for frontend applications and third-party integrations. Ensuring these APIs are secure and performant is a daily priority.
• Collaboration: You will work closely with Product Managers and UI/UX designers to translate requirements into technical specifications. The role requires active participation in agile ceremonies and code reviews.
• System Reliability: You will be responsible for the health of your services, debugging production issues, and optimizing database queries to handle large datasets efficiently.

To succeed in this interview process and the role itself, you should align with the following requirements:

• Technical Skills:
  • Strong proficiency in Java is highly preferred.
  • Experience with Spring Boot or similar application frameworks.
  • For full-stack roles, experience with modern JavaScript frameworks, specifically Angular.
  • Solid understanding of SQL and relational database concepts.
• Experience Level:
  • Typically requires a BS or MS in Computer Science or equivalent experience.
  • Proven experience working on enterprise-level SaaS applications or complex distributed systems.
• Soft Skills:
  • Ability to communicate technical concepts to non-technical stakeholders.
  • A proactive approach to problem-solving and a willingness to ask questions when requirements are ambiguous.

Q: How difficult are the coding questions? Most candidates rate the difficulty as Medium. You generally won't face obscure dynamic programming puzzles, but you must be comfortable with arrays, strings, hash maps, and basic graph logic. The focus is on clean, working code rather than trick questions.

Q: What is the timeline for the interview process? The process can take anywhere from 3 to 6 weeks. Candidates have reported varying timelines, with some experiencing delays between the onsite and the final decision. It is important to be patient but persistent.

Q: Is the interview mostly remote or in-person? While Castlight has physical offices (e.g., San Francisco, Hyderabad), the majority of recent interview loops have been conducted virtually via video calls and shared coding environments.

Q: What happens if I don't hear back after a round? Unfortunately, communication delays have been a reported pain point. If you have not heard back within a week of your interview, it is acceptable and recommended to politely follow up with your recruiter.

Clarify Before You Code In the coding rounds, interviewers often present problems that require clarification. Do not jump straight into coding. Ask about edge cases, input constraints, and expected output. This mimics the "discussion" style they value.

Brush Up on Frameworks Unlike generalist tech companies that only care about algorithms, Castlight interviews often drift into specific framework knowledge (Spring/Angular). Review your annotations, dependency injection concepts, and API design principles before the interview.

Be Proactive with Communication

Know Your Resume Inside Out Expect deep questions about the projects listed on your resume. If you claim knowledge of a specific tool or architecture, be ready to defend your design choices and explain what you would do differently today.

Prepare for the "Why Healthcare?" Question Castlight is mission-driven. demonstrating a genuine interest in solving healthcare navigation problems can set you apart from candidates who are just looking for "any" software job.

Interviewing for a Software Engineer position at Castlight is an opportunity to join a team tackling meaningful challenges in the healthcare industry. The process is designed to find engineers who are not only technically sound in Java, Spring, and System Design but also collaborative and mission-oriented. By preparing for a mix of algorithmic problem-solving and practical framework discussions, you can position yourself as a strong candidate.

Focus your preparation on medium-level LeetCode problems, REST API design, and being able to clearly articulate your past engineering decisions. Remember that the interview is a two-way conversation; use it to demonstrate your communication skills and your ability to work through problems as part of a team.

The salary data above provides a baseline for compensation expectations. Keep in mind that total compensation at Castlight may include equity components and performance bonuses, which can vary based on your experience level and location. Good luck with your preparation!