Kredily Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers at Indian SaaS and B2B product companies build and maintain the server-side systems that power multi-tenant web applications. Day to day, they write APIs, design database schemas, integrate with third-party services, and ensure that features like payroll processing or employee management work reliably for hundreds of business customers. They also debug production issues, optimise slow queries, and collaborate with frontend and product teams to ship new features quickly.

Role and technical knowledge

1. 1

   What is a REST API and how would you design one for a simple employee leave management feature?

   Cover resources like /employees and /leaves, use of HTTP methods (GET, POST, PUT, DELETE), status codes, and JSON request/response formats. Mention versioning and authentication if relevant.

2. 2

   Explain the difference between SQL and NoSQL databases. Which would you choose for storing payroll data and why?

   Highlight that payroll needs strong consistency, transactions, and complex queries, so SQL is often preferred. Acknowledge that NoSQL can work for flexible schemas but may need extra effort for ACID compliance.

3. 3

   How does JWT-based authentication work in a multi-tenant SaaS application?

   Describe token generation on login, signing with a secret, sending in Authorization header, and verifying on each request. Mention tenant isolation by including tenant ID in the token or checking against the user's organisation.

4. 4

   What are database indexes and when would you add one? Give an example from a B2B product.

   Explain that indexes speed up reads but slow down writes. Example: adding an index on employee_id in an attendance table to quickly fetch records for a specific employee.

Practical scenarios and problem solving

1. 5

   A customer reports that their payroll report is taking too long to load. How would you debug and fix this?

   Start by checking logs and query execution time, look for missing indexes or N+1 queries, consider caching or pagination, and test with a smaller dataset. Communicate findings to the customer support team.

2. 6

   You need to integrate a third-party payment gateway for subscription billing. What steps would you take?

   Outline reading API docs, setting up webhooks for payment status, handling failures and retries, storing transaction IDs, and ensuring idempotency to avoid double charging.

3. 7

   How would you handle a situation where two users from different companies try to access the same resource ID?

   Explain tenant isolation: always verify that the resource belongs to the user's organisation before returning data. Use middleware or guards to enforce this on every request.

4. 8

   Describe how you would implement a simple rate limiter for an API endpoint to prevent abuse.

   Mention using a token bucket or sliding window with Redis, returning 429 status when limit exceeded, and setting limits per user or per IP. Discuss trade-offs between strictness and user experience.

Behavioural and teamwork

1. 9

   Tell me about a time you had to learn a new technology quickly for a project. How did you approach it?

   Use a specific example from college or internship. Show steps: reading docs, building a small prototype, asking for help, and applying it to the project. Emphasise curiosity and self-learning.

2. 10

   Describe a situation where you disagreed with a teammate on a technical approach. How did you resolve it?

   Focus on listening to their perspective, presenting data or pros/cons, and reaching a consensus. Avoid blaming; show respect and willingness to compromise for the project's benefit.

3. 11

   In a fast-growing SaaS company, priorities can change quickly. How do you handle shifting requirements?

   Highlight adaptability, asking clarifying questions, breaking work into smaller tasks, and communicating progress. Mention keeping code modular to accommodate changes.

4. 12

   Why do you want to work in a B2B SaaS product company rather than a consumer tech company?

   Show interest in solving business problems, working with multiple stakeholders, and building features that directly impact other companies' operations. Mention desire to learn about domains like HR, payroll, or CRM.

HR and company fit

1. 13

   What do you know about our company and what we do?

   Research the company's product, target customers, and recent news. For a company like Kredily, mention HR and payroll software for Indian businesses. Show genuine interest.

2. 14

   Where do you see yourself in the next two years as a backend engineer?

   Align your goals with the company's needs: becoming proficient in the tech stack, taking ownership of modules, and contributing to scalable architecture. Avoid saying you want to leave for higher studies.

3. 15

   How do you handle working under tight deadlines, especially during a product launch?

   Talk about prioritising tasks, communicating early if something is at risk, and focusing on delivering a working core first. Mention staying calm and using time management techniques.

4. 16

   What are your salary expectations for this role?

   Research typical fresher salaries in Indian SaaS startups. Give a range based on your skills and location, and express flexibility. Emphasise that learning and growth are more important than the exact number.