As a Software Engineer at 3Pillar, you are not just writing code; you are a critical contributor to the design and implementation of high-impact digital products. 3Pillar specializes in product development, meaning your work directly influences the end-user experience and the business outcomes for a diverse set of clients. You will often find yourself working in cross-functional, collaborative teams where your technical expertise helps bridge the gap between complex business requirements and scalable, elegant software solutions. This role requires a blend of deep technical proficiency and a product-focused mindset. Whether you are working with Java, C#.NET, Python, or modern frontend frameworks like React and Angular, you will be expected to contribute to the entire software development lifecycle. You will participate in architecture discussions, tackle challenging bugs, and collaborate closely with product managers and designers to ensure that the technical solutions you build are both robust and aligned with the long-term vision of the product.
Screening Call
reportedInitial call to establish alignment on your background and the role requirements.
What to demonstrate
- Initial call to establish alignment on your background and the role requirements
- Depth in React
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 Evaluations
reportedIncludes coding challenges or deep-dive discussions on your past projects.
What to demonstrate
- Includes coding challenges or deep-dive discussions on your past projects
- Depth in React
How to prepare
- Answer aloud and timed: What are the key principles of Object-Oriented Programming (OOP), and how do you implement them?
- Answer aloud and timed: How do you approach optimizing code that is underperforming?
Behavioral Interviews
reportedInterviews focused on understanding your engineering philosophy and team culture contribution.
What to demonstrate
- Interviews focused on understanding your engineering philosophy and team culture contribution
- Depth in React
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 interviews above and write down what you would ask to confirm before it.
PracHub editorial advice for the preparation topics above.
Be prepared to talk about your code
Don't just show that you can write it; be ready to explain the trade-offs you made and why you chose a specific approach.
Ask meaningful questions
Use the interview to learn about the team's challenges and the product's roadmap. This shows you are genuinely interested in the business impact of your work.
Stay calm under pressure
If you get stuck on a coding problem, communicate your thought process clearly to the interviewer. They are often looking for how you respond to ambiguity.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Explain the difference between synchronous and asynchronous programming in your primary language.
Explain the difference between synchronous and asynchronous programming in your primary language.
Approach
- Say what the runtime actually does before reasoning about the code.
- Name what is shared across threads and what owns each piece of state.
- Identify the window where an invariant is briefly untrue.
- 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?
Write a function to implement a common sorting algorithm.
Write a function to implement a common sorting 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?
Given a specific scenario, how would you handle a memory-intensive operation?
Given a specific scenario, how would you handle a memory-intensive operation?
Approach
- Say what the runtime actually does before reasoning about the code.
- Name what is shared across threads and what owns each piece of state.
- Identify the window where an invariant is briefly untrue.
- 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?
Can you demonstrate how to implement a specific feature using common design patterns?
Can you demonstrate how to implement a specific feature using common design patterns?
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 time and space complexity of the solution you just wrote.
Explain the time and space complexity of the solution you just wrote.
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?
Stop tag and share joins from fanning out a page
resource_tag is (resource_id, tag_id) with PK (resource_id, tag_id); resource_share is (resource_id, shared_with_user_id, permission). The tagged-and-shared listing inner-joins resource to both, filters tenant_id, tag_id = ANY($2) and shared_with_user_id = $3, orders by updated_at DESC and takes 50. Pages come back with fewer than 50 distinct resources and the total in the header is far too high. Explain the row multiplication, rewrite both the page query and the count query so each is correct, and name the index each one needs. PostgreSQL 16.
Approach
- Do the arithmetic against the predicates that are actually there. An inner join emits one row per matching child row, and both joins are filtered: tag_id = ANY($2) admits only the requested tags, shared_with_user_id = $3 admits one user's share rows. So a resource holding three of the requested tags and shared with $3 once yields three rows, not one — the multiplier is its count of matching tags times its share rows for that single user, and that second factor is 1 unless the table admits duplicate (resource_id, shared_with_user_id) pairs. LIMIT 50 then limits rows rather than resources, and COUNT(*) counts pairs — the header is the product, not the population.
- Reject DISTINCT as the fix. It deduplicates after the product has been built, so the planner must materialise and sort the fanned-out set before the LIMIT can apply, and it leaves any SUM or AVG in the same select list wrong.
- Rewrite both filters as semi-joins, keeping resource as the only row source: AND EXISTS (SELECT 1 FROM resource_tag rt WHERE rt.resource_id = r.resource_id AND rt.tag_id = ANY($2)) and the same shape against resource_share. A semi-join stops at the first match per resource and preserves the driving index order, so ORDER BY updated_at DESC, resource_id DESC LIMIT 50 still stops after 50 rows.
- Count with the same predicates and no join at all: SELECT count(*) FROM resource r WHERE r.tenant_id = $1 AND r.status = 'active' AND EXISTS (...) AND EXISTS (...). Nothing multiplies a resource, so the number is the population.
Follow-up
- The filter changes from 'any of these tags' to 'all of these tags'. Rewrite it and state what it costs relative to the ANY form.
- A resource can be shared with the same user twice under different permissions. Does your count change, and should it?
Keep soft-deleted accounts from blocking re-registration
app_user holds user_id, tenant_id, email CITEXT, password_hash (NULL for SSO principals), email_verified_at, auth_version, status ('invited','active','suspended','deactivated'), created_at, updated_at, deleted_at. Two live accounts for one address inside a tenant must be impossible, but an address freed by a soft delete must be reusable, and the same tenant may delete and re-register it repeatedly. Write the uniqueness DDL for PostgreSQL 16, then the equivalent for MySQL 8 where partial indexes do not exist, and say what each permits once three deleted rows already hold that address.
Approach
- Start from what is actually unique: not (tenant_id, email), but (tenant_id, email) among live rows. PostgreSQL says that directly — CREATE UNIQUE INDEX app_user_live_email ON app_user (tenant_id, email) WHERE deleted_at IS NULL. A full constraint over the same two columns burns the address permanently the first time someone deletes an account.
- Keep case-insensitivity in the type or the index, never in the application: CITEXT as given, or UNIQUE (tenant_id, lower(email)) as an expression index where the extension is unavailable. A case-sensitive unique column is exactly how two accounts for one human appear.
- For MySQL 8 the predicate has to move inside the key: add a discriminator column that is a constant 0 while the row is live and is set to user_id on delete, with UNIQUE (tenant_id, email, deleted_marker). Live rows share the constant and still collide; deleted rows differ from each other and stop colliding.
- State the NULL variant and its dependency: leaving the marker NULL for deleted rows also works, because a unique index treats NULLs as distinct — true in MySQL, and true in PostgreSQL only under the default NULLS DISTINCT, which PostgreSQL 15 lets you reverse. Check the polarity against the three existing deleted rows: constant-on-live is what preserves the collision you want, and reversing it silently admits duplicate live accounts.
Follow-up
- A deleted account re-registers with the same address the next day. Do the old resource rows follow the new user_id, and how does the API keep the two principals apart?
- How do you honour an erasure request while resource_revision.actor_user_id still references this table?
Explain how data passes between components in your preferred framework.
Explain how data passes between components in your preferred framework.
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 the difference between various data structures and when you would choose one over the other.
Describe the difference between various data structures and when you would choose one over the other.
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 are the key principles of Object-Oriented Programming (OOP), and how do you implement them?
What are the key principles of Object-Oriented Programming (OOP), and how do you implement them?
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 do you approach optimizing code that is underperforming?
How do you approach optimizing code that is underperforming?
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 your process for debugging a complex issue reported by a client.
Describe your process for debugging a complex issue reported by a client.
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 3Pillar candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the 3Pillar loop
- Write out the reported sequence: Screening Call, Technical Evaluations, Behavioral Interviews.
- 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 React
- Spend the session on React, which 3Pillar candidates report being tested on.
- Write one worked example in React and time yourself on it.
Deliverable: One timed worked example in React.
03Work Data Structures & Algorithms (DSA)
- Spend the session on Data Structures & Algorithms (DSA), which 3Pillar candidates report being tested on.
- Write one worked example in Data Structures & Algorithms (DSA) and time yourself on it.
Deliverable: One timed worked example in Data Structures & Algorithms (DSA).
04Work JavaScript
- Spend the session on JavaScript, which 3Pillar candidates report being tested on.
- Write one worked example in JavaScript and time yourself on it.
Deliverable: One timed worked example in JavaScript.
05Answer out loud: Technical and Domain Knowledge
- Answer aloud, timed: Explain how data passes between components in your preferred framework.
- Answer aloud, timed: Describe the difference between various data structures and when you would choose one over the other.
Deliverable: Spoken answers to 2 reported Technical and Domain Knowledge question(s), under time.
06Answer out loud: Coding and Algorithms
- Answer aloud, timed: Write a function to implement a common sorting algorithm.
- Answer aloud, timed: Given a specific scenario, how would you handle a memory-intensive operation?
Deliverable: Spoken answers to 2 reported Coding and Algorithms question(s), under time.
07Answer out loud: Behavioral and Managerial
- Answer aloud, timed: Describe a time you had a disagreement with a team member; how did you resolve it?
- Answer aloud, timed: Tell us about a project where you had to learn a new technology on the fly.
Deliverable: Spoken answers to 2 reported Behavioral and Managerial 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 you had a disagreement with a team member; how did you resolve it?
Describe a time you had a disagreement with a team member; how did you resolve it?
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?
Tell us about a project where you had to learn a new technology on the fly.
Tell us about a project where you had to learn a new technology on the fly.
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 tight deadlines and shifting priorities?
How do you handle tight deadlines and shifting priorities?
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?
Describe a situation where you had to explain a technical issue to a non-technical stakeholder.
Describe a situation where you had to explain a technical issue to a non-technical stakeholder.
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 stay updated with the latest industry trends?
What motivates you to stay updated with the latest industry trends?
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 you had a disagreement with a team member; how did you resolve it?
- 02
Tell us about a project where you had to learn a new technology on the fly.
- 03
How do you handle tight deadlines and shifting priorities?
- 04
Describe a situation where you had to explain a technical issue to a non-technical stakeholder.
How difficult is the interview process?
Candidates generally describe the process as moderate to challenging. The focus is on practical application rather than theoretical trick questions, so deep knowledge of your craft is your best asset.
3Pillar Software Engineer candidate reports ↗How long does the process take?
The typical timeline from initial contact to a final decision is roughly 1–2 weeks, though this can vary based on project urgency.
3Pillar Software Engineer candidate reports ↗Is the technical assessment done on a whiteboard or a computer?
Most technical assessments today are conducted online, often involving screen-sharing where you will code in your preferred environment.
3Pillar Software Engineer candidate reports ↗What is the company culture like?
3Pillar values a collaborative, professional, and product-driven environment. We look for individuals who are curious, communicative, and committed to delivering high-quality results.
3Pillar Software Engineer candidate reports ↗What topics does 3Pillar test in interviews?
3Pillar interviews most often cover Problem Solving, JavaScript, System Design, Data Modeling, and Scalability. The exact emphasis depends on the specific role you apply for.
3Pillar Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.
- 013Pillar Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
Candidate reports · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
PracHub page · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
PracHub page · Accessed 2026-09-22
Explore related engineering environments and compare the preparation focus.
Vercel Software Engineer Interview Guide
Debugging practice for Vercel software engineer prep built on a reproduction you trust, narrowing to the smallest failing input, and changing one variable per run so the result stays attributable.
Spotify Software Engineer Interview Guide
Timed practice for Spotify software engineer candidates who lose time to the clock: short problems taken end to end, then reviewed against a written rubric rather than a passing test run.
Shopify Software Engineer Interview Guide
Timed practice for Shopify software engineer candidates who lose time to the clock: short problems taken end to end, then reviewed against a written rubric rather than a passing test run.
Ramp Software Engineer Interview Guide
Systems practice for Ramp software engineer candidates, weighted toward payments and lending work: the load that actually arrives, the failure modes that matter there, and the invariants a partial outage must not break.