BehavioralMediumBehavioral
Tell me about a problem you prevented before it reached production.
Show how you noticed a risk early, validated it, communicated it and added a safeguard.
Mid-level 路 Senior 路 Behavioral Interviews
Backend Developer 路 Intern to senior
Backend Developer Interview Questions and Answers
Backend interviews test how you store, process and serve data reliably: language fundamentals, SQL and indexing, concurrency, API design and how systems behave under load.
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131 questions
- BehavioralMediumBehavioral
Tell me about a time you had to work with a difficult stakeholder.
Describe how you understood the stakeholder鈥檚 goals, handled disagreement professionally and reached a workable outcome.
Mid-level 路 Senior 路 Behavioral Interviews - Node.jsHard
How do you secure a Node.js Express API?
Validate all input, use parameterised queries, add security headers with helmet, rate-limit requests, restrict CORS, hash passwords, keep secrets in environment variables, and keep dependencies updated and audited.
Mid-level 路 Senior 路 Security - JavaHard
What is the difference between HashMap, Hashtable and ConcurrentHashMap in Java?
HashMap is not thread-safe, Hashtable is thread-safe by locking the whole map on every method, and ConcurrentHashMap is thread-safe with much finer-grained locking and lock-free reads, so it scales far better.
Mid-level 路 Senior 路 Data Structures - JavaHard
How does JVM memory management and garbage collection work in Java?
The JVM divides memory into a per-thread stack, a shared heap (split into young and old generations) and Metaspace; the garbage collector frees heap objects that are no longer reachable, collecting short-lived young objects frequently and old objects less often.
Mid-level 路 Senior 路 Memory Management - BehavioralHardBehavioral
Tell me about a technical debt decision you made.
Explain why you accepted, reduced or paid down technical debt and how you managed the associated risk.
Mid-level 路 Senior 路 Behavioral Interviews - BehavioralHardBehavioral
Tell me about a time you introduced a new technology or tool to a project.
Start with the problem, evaluate alternatives, validate the technology with a small experiment and explain how you managed adoption and risk.
Mid-level 路 Senior 路 Behavioral Interviews - BehavioralMediumBehavioral
Tell me about a time you mentored or helped another developer grow.
Explain how you identified what the developer needed, coached rather than simply solved the problem, and measured their progress.
Senior 路 Behavioral Interviews - TypeScriptHard
What are mapped types and conditional types in TypeScript?
Mapped types build a new object type by looping over keys (`{ [K in keyof T]: ... }`). Conditional types pick a result with `T extends U ? X : Y`, which is how many utility types are implemented.
Senior 路 Types & Type System - Node.jsHard
How do you scale a Node.js application and avoid blocking the event loop?
Keep the main thread free by moving CPU-heavy work to worker threads or a job queue, and scale across cores and machines by running multiple processes (cluster or PM2) behind a load balancer with shared, external state.
Senior 路 Performance - SQLHard
What are transaction isolation levels in SQL and what problems do they prevent?
Isolation levels (Read Uncommitted, Read Committed, Repeatable Read, Serializable) control how much concurrent transactions can see of each other's changes, trading consistency against concurrency to prevent dirty reads, non-repeatable reads and phantom reads.
Senior 路 Database - SQLHard
How do you optimize a slow SQL query?
Read the execution plan with EXPLAIN to find full scans and expensive joins, add or fix indexes for the filter and join columns, select only the columns and rows you need, and rewrite predicates so indexes can be used.
Senior 路 Performance - C#Hard
How do you avoid deadlocks with async/await in C#?
Use async all the way down instead of blocking on tasks with .Result or .Wait(), and in library code use ConfigureAwait(false) so continuations do not need to return to a captured context.
Senior 路 Asynchronous Programming - JavaHard
What is the difference between synchronized and volatile in Java, and how do you avoid deadlocks?
synchronized gives mutual exclusion and memory visibility for a block of code, while volatile only guarantees that reads and writes of one variable are visible to all threads and does not make compound operations such as count++ atomic.
Senior 路 Concurrency - PythonHard
What is the GIL in Python and how does it affect multithreading?
The Global Interpreter Lock (GIL) in CPython lets only one thread execute Python bytecode at a time, so threads do not speed up CPU-bound code but still help with I/O-bound work.
Senior 路 Concurrency - PythonHard
What is the difference between threading, multiprocessing and asyncio in Python?
Threading runs concurrent threads that share memory and suit blocking I/O, multiprocessing runs separate processes to use multiple CPU cores for CPU-bound work, and asyncio runs many non-blocking tasks cooperatively on one thread for high-volume I/O.
Senior 路 Concurrency - System DesignHardSystem design
How do you design a URL shortener like bit.ly?
Generate a short unique code for each long URL (for example by base62-encoding a unique ID), store the mapping in a key-value or relational database, serve redirects through a cache because reads far outnumber writes, and record analytics asynchronously.
Senior 路 System Design - System DesignHard
What is the CAP theorem and what does it mean in practice?
The CAP theorem says that during a network partition a distributed system must choose between consistency (every read sees the latest write) and availability (every request gets a response); you cannot have both while the partition lasts.
Senior 路 System Design - System DesignHard
What is the difference between database sharding and replication?
Replication copies the same data to several servers to improve read capacity and availability, while sharding splits the data across servers so each holds only a part, which increases write capacity and total storage.
Senior 路 Database - System DesignHard
Monolith vs microservices: which should you choose?
Start with a well-structured monolith unless you have several teams and clear service boundaries, because microservices add distributed-system complexity such as network failures, data consistency and operational overhead.
Senior 路 Architecture