cswork / libraryOpen practice workspace

Interview guides · Taboola

Taboola Software Engineer Interview Guide

Taboola Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

Taboola hires Software Engineers; this guide collects what candidates report about the process.

This guide is scoped to a Software Engineer candidate at Taboola.

Focus areas

  • Data Structures
  • Algorithms
  • Time Complexity Analysis

The Taboola interview process

Taboola candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Initial Screening

Align on technical expectations through a preliminary discussion.

What to demonstrate

  • Align on technical expectations through a preliminary discussion
  • Depth in Data Structures

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

Participate in a series of deep-dive technical interviews covering algorithmic challenges.

What to demonstrate

  • Participate in a series of deep-dive technical interviews covering algorithmic challenges
  • Depth in Data Structures

How to prepare

  • Answer aloud and timed: Describe how you would implement a thread-safe cache or a concurrent hash map.
  • Answer aloud and timed: Explain the difference between asynchronous functions and synchronous execution in your preferred language.

Home Assignments

Complete assigned tasks or projects to demonstrate technical skills.

What to demonstrate

  • Complete assigned tasks or projects to demonstrate technical skills
  • Depth in Data Structures

How to prepare

  • Answer aloud and timed: How do you calculate the time complexity of a recursive algorithm?
  • Answer aloud and timed: How would you design a recommendation widget similar to the one Taboola uses on news sites?

Project Discussions

Discuss your past projects and experiences in detail.

What to demonstrate

  • Discuss your past projects and experiences in detail
  • Depth in Data Structures

How to prepare

  • Answer aloud and timed: How do you ensure high availability and low latency in a distributed system?
  • Answer aloud and timed: Walk me through a challenging bug you encountered in a production environment and how you diagnosed it.

Where candidates lose points

Clarify Requirements

Always ask clarifying questions before jumping into a coding problem. It demonstrates that you think before acting.

Test Your Code

Always consider edge cases and explain how your code handles them before the interviewer asks.

Stay Professional

Even if you feel the interview is not going well, maintain a collaborative and positive attitude.

Prepare for "Why Taboola?

Have a clear, articulated reason for why you want to work at this company specifically.

Questions & practice

Explain the pros and cons of using an Array versus an ArrayList.

Medium · Technical & Algorithmic Proficiency

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. 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 string, how would you find the first non-repeating character in $O(n)$ time?

Medium · Technical & Algorithmic Proficiency

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. 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?

Describe how you would implement a thread-safe cache or a concurrent hash map.

Medium · Technical & Algorithmic Proficiency

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Explain the difference between asynchronous functions and synchronous execution in your preferred language.

Medium · Technical & Algorithmic Proficiency

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

How do you calculate the time complexity of a recursive algorithm?

Medium · Technical & Algorithmic Proficiency

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. 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 do you approach optimizing a database query that is performing poorly under load?

Medium · System Design & Problem Solving

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. 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?

Explain why the owner filter ignores the listing index

Medium · composite index · query plans · sort elimination

The only index on resource is (tenant_id, status, updated_at DESC, resource_id DESC). A new endpoint returns one user's resources across all statuses, newest created first: WHERE tenant_id = $1 AND owner_user_id = $2 ORDER BY created_at DESC LIMIT 20. On a tenant with 2M rows it takes 900 ms and EXPLAIN shows a sort above a large scan. Explain precisely why the existing index cannot serve it, give the index that can, and state which of these the new index still will not help: owner_user_id alone across tenants; the same query ordered by updated_at. PostgreSQL 16.

Approach

  1. Separate the two jobs an index does. For filtering, a composite btree is seekable only on a left prefix, so with no predicate on status the scan can at best range over tenant_id and test owner_user_id per row; PostgreSQL 16 has no btree skip scan to jump the unconstrained column.
  2. For ordering, the index is sorted by (status, updated_at) within a tenant and not by created_at, so the LIMIT cannot stop early: every matching row is read and then sorted. That is the 'Sort Method: top-N heapsort' line, and it is why the plan reads 2M rows to answer with 20.
  3. Derive the replacement from the access path — equality, equality, then the ordering column: CREATE INDEX CONCURRENTLY ON resource (tenant_id, owner_user_id, created_at DESC). The scan seeks to the (tenant, owner) range and walks 20 entries in order, so the Sort node disappears along with the row-read.
  4. Treat INCLUDE (title, status) as conditional, not free. An index-only scan still visits the heap for any row whose page is not marked all-visible, so on a table taking 1.2k writes/second the win depends on autovacuum keeping the visibility map current, and the wider index costs more on every insert.

Follow-up

  • 90% of rows are status='active'. Would a partial index WHERE status = 'active' change your answer, and for which of the three queries?
  • A dashboard runs this for 40 owners in one page load. What changes about the design?

How would you design a recommendation widget similar to the one Taboola uses on news sites?

Medium · System Design & Problem Solving

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. 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?

How do you ensure high availability and low latency in a distributed system?

Medium · System Design & Problem Solving

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. 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?

Walk me through a challenging bug you encountered in a production environment and how you diagnosed it.

Medium · System Design & Problem Solving

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. 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 a service is experiencing a spike in latency, what steps do you take to identify the root cause?

Medium · System Design & Problem Solving

Approach

  1. Establish what changed and when, before forming any theory.
  2. Pick a bisection that eliminates candidates whichever way it turns out.
  3. Check the instrumentation before believing the symptom.
  4. 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?

Suggested practice checklist

Built from the rounds and topics Taboola candidates report.

Day 1 — Map the Taboola loop

  • Write out the reported sequence: Initial Screening, Technical Interviews, Home Assignments, Project Discussions.
  • 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 4 reported rounds, with the weakest marked.

Day 2 — Work Data Structures

  • Spend the session on Data Structures, which Taboola 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.

Day 3 — Work Algorithms

  • Spend the session on Algorithms, which Taboola candidates report being tested on.
  • Write one worked example in Algorithms and time yourself on it.

Deliverable: One timed worked example in Algorithms.

Day 4 — Work Time Complexity Analysis

  • Spend the session on Time Complexity Analysis, which Taboola candidates report being tested on.
  • Write one worked example in Time Complexity Analysis and time yourself on it.

Deliverable: One timed worked example in Time Complexity Analysis.

Day 5 — Answer out loud: Technical & Algorithmic Proficiency

  • Answer aloud, timed: Explain the pros and cons of using an Array versus an ArrayList.
  • Answer aloud, timed: Given a string, how would you find the first non-repeating character in $O(n)$ time?

Deliverable: Spoken answers to 2 reported Technical & Algorithmic Proficiency question(s), under time.

Day 6 — Answer out loud: System Design & Problem Solving

  • Answer aloud, timed: How would you design a recommendation widget similar to the one Taboola uses on news sites?
  • Answer aloud, timed: How do you ensure high availability and low latency in a distributed system?

Deliverable: Spoken answers to 2 reported System Design & Problem Solving question(s), under time.

Day 7 — Answer out loud: Behavioral & Experience

  • Answer aloud, timed: Tell me about a project where you had to make a significant technical trade-off.
  • Answer aloud, timed: How do you handle disagreements with team members regarding architectural decisions?

Deliverable: Spoken answers to 2 reported Behavioral & Experience question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Tell me about a project where you had to make a significant technical trade-off.

Medium · Behavioral & Experience

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. 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 disagreements with team members regarding architectural decisions?

Medium · Behavioral & Experience

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. 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?

Why are you interested in working at Taboola specifically?

Medium · Behavioral & Experience

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. 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?

Describe a time you had to learn a new technology stack on the fly to meet a project deadline.

Medium · Behavioral & Experience

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. 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?