As a Software Engineer at Viber, you play a crucial role in developing and maintaining the core functionalities that drive our communication platform. Your work directly impacts millions of users worldwide, ensuring that they can connect seamlessly through voice, video, and messaging services. The complexity and scale of the systems you will work on are significant, requiring innovative solutions and a deep understanding of both user needs and technical challenges. This position is critical not just for the technology but for the business itself. By contributing to the development of scalable features, enhancing performance, and ensuring robust security measures, you help shape the user experience and contribute to the overall success of Viber. You will collaborate with cross-functional teams, including product managers and designers, to deliver high-quality products that meet the demands of our diverse user base. Expect to be part of a dynamic environment where you will tackle interesting and challenging problems daily. From optimizing existing features to designing new functionalities, your contributions will help maintain 's status as a leading communication platform. Viber
Initial Screening Call
reportedA call with HR to discuss your background and fit for the role.
What to demonstrate
- A call with HR to discuss your background and fit for the role
- Depth in Algorithms
How to prepare
- Be able to walk your CV end to end in two minutes, and say why this company specifically.
- Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.
Technical Interviews
reportedOne or two interviews that test your coding skills and problem-solving abilities.
What to demonstrate
- One or two interviews that test your coding skills and problem-solving abilities
- Depth in Algorithms
How to prepare
- Answer aloud and timed: Describe a challenging technical problem you faced and how you resolved it.
- Answer aloud and timed: What tools do you use for version control, and why?
Behavioral Interview
reportedDiscussion of your experiences and values to assess cultural fit.
What to demonstrate
- Discussion of your experiences and values to assess cultural fit
- Depth in Algorithms
How to prepare
- Prepare three examples from your own work, each with a decision you made and an outcome you can quantify.
- Re-read the description of the behavioral interview above and write down what you would ask to confirm before it.
PracHub editorial advice for the preparation topics above.
Going into the loop without having done this.
Practice Coding: Regularly practice coding challenges on platforms like LeetCode or HackerRank. This will help you become comfortable with coding interviews.
Going into the loop without having done this.
Understand the Product: Familiarize yourself with Viber’s features and user base. Understanding the product can help you align your answers with the company’s mission.
Going into the loop without having done this.
Engage in Mock Interviews: Consider conducting mock interviews with friends or using platforms like Pramp. This practice can reduce anxiety and improve your performance.
Going into the loop without having done this.
Ask Questions: Prepare thoughtful questions about the team dynamics and project expectations. This shows your interest and helps assess if it's the right fit for you.
Going into the loop without having done this.
Stay Calm: During technical interviews, don’t rush through problems. Take your time to think through your approach and communicate your thought process clearly.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Write a function to reverse a string.
Write a function to reverse a string.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
How would you implement a binary search algorithm?
How would you implement a binary search algorithm?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Explain the differences between a stack and a queue.
Explain the differences between a stack and a queue.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Given a list of integers, write a function to find the two numbers that add up to a specific target.
Given a list of integers, write a function to find the two numbers that add up to a specific target.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
What are the trade-offs between SQL and NoSQL databases?
What are the trade-offs between SQL and NoSQL databases?
Approach
- Name the grain you start from and join outward from it.
- Check whether any join is one-to-many before aggregating, or the sums inflate.
- Say which index the query would use, and what makes it unusable.
- Handle the rows that do not match: that is usually the actual question.
Follow-up
- How does the query change if that join becomes one-to-many?
- What happens to this when the table is ten times larger?
Find version gaps and relay lag with window functions
outbox_event holds event_id, aggregate_type, aggregate_id, aggregate_version, event_type, payload, status ('pending','published','dead'), attempts, created_at, published_at. A projection is missing rows and you must decide whether the relay skipped events or the consumer dropped them. Write three queries over the last seven days: one listing every aggregate_id whose published aggregate_version sequence has a hole, one giving per-day counts with a running total, and one returning the newest published event per aggregate. For each, say where the window function is evaluated relative to WHERE and LIMIT. PostgreSQL 16.
Approach
- Gaps: compute lead(aggregate_version) OVER (PARTITION BY aggregate_id ORDER BY aggregate_version) in a subquery, then filter next_version <> aggregate_version + 1 in the outer query. Window functions are evaluated after WHERE, GROUP BY and HAVING and before the outer ORDER BY and LIMIT, so the predicate cannot sit in the same WHERE clause and PostgreSQL 16 has no QUALIFY.
- Say what the seven-day filter does to the answer: it truncates every partition, so the first row per aggregate has no predecessor inside the window and a hole spanning the boundary is invisible. Widen the window, or join to resource.version as the authority for the true maximum.
- Running total: SELECT date_trunc('day', created_at) AS d, count() AS n, sum(count()) OVER (ORDER BY date_trunc('day', created_at) ROWS UNBOUNDED PRECEDING). An aggregate inside a window call is legal because grouping runs before windowing. The grouping key is unique per row here so ROWS and RANGE agree, but write the frame anyway — over ungrouped rows with tied timestamps the default RANGE frame pulls in every peer row and the total jumps.
- Newest per aggregate: DISTINCT ON (aggregate_id) ... ORDER BY aggregate_id, aggregate_version DESC is the cheap PostgreSQL-only form when an index matches that order; row_number() OVER (PARTITION BY aggregate_id ORDER BY aggregate_version DESC) = 1 is the portable form and needs a subquery for the same evaluation-order reason as the gap query.
Follow-up
- Relay failover redelivers events. Does a duplicate break the gap query, and how would you detect one from this table alone?
- Turn the gap check into a continuous monitor rather than a query someone runs after an incident. What does it watch?
What programming languages are you most comfortable with, and why?
What programming languages are you most comfortable with, and why?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Can you explain the concept of object-oriented programming?
Can you explain the concept of object-oriented programming?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Describe a challenging technical problem you faced and how you resolved it.
Describe a challenging technical problem you faced and how you resolved it.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What tools do you use for version control, and why?
What tools do you use for version control, and why?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How would you design a messaging system for real-time communication?
How would you design a messaging system for real-time communication?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Discuss the considerations for scaling a microservices architecture.
Discuss the considerations for scaling a microservices architecture.
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
If given a new feature request, what steps would you take to implement it?
If given a new feature request, what steps would you take to implement it?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How would you approach debugging a production issue?
How would you approach debugging a production issue?
Approach
- Establish what changed and when, before forming any theory.
- Pick a bisection that eliminates candidates whichever way it turns out.
- Check the instrumentation before believing the symptom.
- Separate the trigger from the cause; the deploy is rarely the bug.
Follow-up
- What would you look at first, and what would it rule out?
- How would you tell a cause from a coincidence here?
Built from the rounds and topics Viber candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Viber loop
- Write out the reported sequence: Initial Screening Call, Technical Interviews, Behavioral Interview.
- For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.
Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.
02Work Algorithms
- Spend the session on Algorithms, which Viber candidates report being tested on.
- Write one worked example in Algorithms and time yourself on it.
Deliverable: One timed worked example in Algorithms.
03Work Data Structures
- Spend the session on Data Structures, which Viber candidates report being tested on.
- Write one worked example in Data Structures and time yourself on it.
Deliverable: One timed worked example in Data Structures.
04Work Golang (Go)
- Spend the session on Golang (Go), which Viber candidates report being tested on.
- Write one worked example in Golang (Go) and time yourself on it.
Deliverable: One timed worked example in Golang (Go).
05Answer out loud: Technical / Domain Questions
- Answer aloud, timed: What programming languages are you most comfortable with, and why?
- Answer aloud, timed: Can you explain the concept of object-oriented programming?
Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.
06Answer out loud: Coding / Algorithms
- Answer aloud, timed: Write a function to reverse a string.
- Answer aloud, timed: How would you implement a binary search algorithm?
Deliverable: Spoken answers to 2 reported Coding / Algorithms question(s), under time.
07Answer out loud: System Design / Architecture
- Answer aloud, timed: How would you design a messaging system for real-time communication?
- Answer aloud, timed: Discuss the considerations for scaling a microservices architecture.
Deliverable: Spoken answers to 2 reported System Design / Architecture question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
Describe a time when you had to work collaboratively to solve a problem.
Describe a time when you had to work collaboratively to solve a problem.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
How do you handle criticism or feedback on your work?
How do you handle criticism or feedback on your work?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
What motivates you to excel as a software engineer?
What motivates you to excel as a software engineer?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
- 01
Describe a time when you had to work collaboratively to solve a problem.
- 02
How do you handle criticism or feedback on your work?
- 03
What motivates you to excel as a software engineer?
What is the interview difficulty level and how much preparation time is typical?
The interview process at Viber is generally considered average to difficult. Candidates typically spend 2-4 weeks preparing, focusing on technical skills and behavioral questions.
Viber Software Engineer candidate reports ↗What differentiates successful candidates?
Successful candidates demonstrate strong technical skills, a collaborative spirit, and a clear alignment with Viber’s values. Highlighting past experiences that show your problem-solving abilities can make a significant difference.
Viber Software Engineer candidate reports ↗What is the culture and working style at Viber?
Viber promotes a culture of innovation and collaboration, where team members are encouraged to share ideas and work together towards common goals. Expect a supportive environment that values diversity and inclusion.
Viber Software Engineer candidate reports ↗What is the typical timeline from initial screen to offer?
The hiring process generally takes 3-6 weeks, depending on the number of interview rounds and candidate availability.
Viber Software Engineer candidate reports ↗Are there remote work or hybrid expectations?
Depending on the role and location, Viber offers flexible work arrangements, including remote and hybrid options. Be prepared to discuss your preferences during the interview.
Viber Software Engineer candidate reports ↗How hard is the Viber interview?
Candidates most commonly rate Viber interviews as medium, based on 80 reported interviews. About 43% of candidates who interview go on to receive an offer.
Viber Software Engineer candidate reports ↗What topics does Viber test in interviews?
Viber interviews most often cover Problem Solving, Stakeholder Communication, Communication Skills, System Design, and Interview Process Navigation. The exact emphasis depends on the specific role you apply for.
Viber Software Engineer candidate reports ↗Is Viber a good place to work?
Employees rate Viber 4.5 out of 5 overall, based on aggregated workplace reviews spanning career growth, work-life balance, compensation, culture, and management.
Viber Software Engineer candidate reports ↗Where is Viber headquartered?
Viber is headquartered in Luxembourg, Luxembourg.
Viber Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
Official role evidence, timestamped platform data and clearly labeled preparation advice.
- 01Viber Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
candidate · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
platform · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
platform · Accessed 2026-09-22
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