Backend Developer
Practice APIs, databases, caching, auth and system design questions asked in Backend Developer interviews, from HTTP basics to distributed systems.
- Questions
- 100
- Interview Qs
- 30
- Judged problems
- 211
- Skills
- 9
About the role
A Backend Developer builds the part of an application that users do not see: the APIs, business logic, databases and background jobs that power web and mobile apps. On a normal day you design and build REST or GraphQL endpoints, write SQL and data models, connect to third-party services like payment gateways, and fix bugs reported from production.
The job is about correctness, security and scale. You must make sure data is never lost or corrupted, that only the right users can access the right data, and that the system stays fast when traffic grows from a hundred users to a million. That means understanding indexes, transactions, caching, queues and how to read logs and metrics when something goes wrong.
As you grow, you design whole services, choose databases and infrastructure, review other engineers' code, plan migrations without downtime, and take part in on-call so you can respond quickly when production has a problem.
Practise by level
Open the full question bank (100 questions) →Mock interview
Screening round
4 questions · 4 min each · pass 50%
mediumTechnical round
5 questions · 4 min each · pass 60%
hardFinal round
6 questions · 3 min each · pass 70%
Coding problems for backend developers
- Add Two Binary Stringseasy
- Alphanumeric Palindrome Checkeasy
- Balance Point of a Beameasy
- Balanced Bracket Stringeasy
- Banner From Letter Tileseasy
- Best K-Day Sales Windoweasy
- Best Single Trade Profiteasy
- Can One Person Attend Every Booking?easy
- Cancel Adjacent Twinseasy
- Collapse Repeated Readingseasy
- Compare Release Versionseasy
- Compress Character Runseasy
SQL problems
- Account Balance Tierseasy
- Customers Who Never Orderedeasy
- Department Headcounteasy
- Duplicate Signup Emailseasy
- Employees Without a Managereasy
- High-Value Delivered Orderseasy
- Late Shipmentseasy
- Total Successful Paymentseasy
- User Display Nameseasy
- Wishlist Items Also in Carteasy
Skills in this track
Learning roadmap
- 1
One language and the web basics
Pick one backend language such as JavaScript/TypeScript (Node.js), Python, Java or Go. Learn how HTTP works: methods, status codes, headers, cookies and JSON.
- 2
Build REST APIs with a framework
Use Express or Fastify, Django or FastAPI, Spring Boot or Go net/http. Build CRUD APIs with validation, error handling, pagination and automated tests.
- 3
Databases in depth
Learn PostgreSQL or MySQL well: schema design, joins, indexes, transactions and isolation levels. Then learn when a NoSQL store like MongoDB or Redis is a better fit.
- 4
Auth, security and caching
Implement sessions and JWT, password hashing, role-based access and rate limiting. Add Redis caching and learn cache invalidation and the OWASP Top 10.
- 5
Async work and deployment
Use queues like RabbitMQ, Kafka or SQS for background jobs. Containerize with Docker, deploy to a cloud provider, and add logs, metrics and alerts.
- 6
System design and portfolio
Study scaling patterns: replication, sharding, load balancing, idempotency and event-driven design. Build 2 to 3 real projects and explain their trade-offs clearly.
Top Backend Developer interview questions
- How would you design a REST API for a simple blog with posts and comments? Mention URLs, methods and status codes.
- When would you choose a SQL database and when a NoSQL database?
- What is the difference between authentication and authorization? How would you implement both in an API?
- Explain what happens on the backend from the moment a request hits your server until a response is sent.
- What is a database index, and what are its costs? How do you decide which columns to index?
- What is a database transaction, and what do the letters in ACID mean? Give an example where you need one.