As a Software Engineer at The Lab, you will play a pivotal role in transforming innovative ideas into functional digital products that engage users and drive business success. This role is essential to our mission of delivering fast-paced, high-quality web and e-commerce solutions that meet the evolving needs of our diverse clientele. You will work on dynamic projects that blend creativity and technology, ensuring that your contributions significantly impact both the user experience and the overall effectiveness of our products. The position is critical for maintaining the high standards of quality and performance that our clients expect. You will collaborate with a talented team of strategists, creatives, and developers, driving projects from conceptual design through to launch and beyond. Your work will not only involve technical problem-solving but will also require a deep understanding of user experience, e-commerce flows, and web development processes, making this role both challenging and rewarding. Expect to engage with cutting-edge technologies and frameworks while bringing your unique perspective to a collaborative environment that values creativity and innovation. You will have the opportunity to influence product development and contribute to projects that push boundaries, making your role at both exciting and strategically significant. The Lab
Initial Screening
reportedThe first step involves a review of your application and qualifications.
What to demonstrate
- The first step involves a review of your application and qualifications
- Depth in Web Project Management
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 Assessment
reportedCandidates undergo technical assessments to evaluate their skills.
What to demonstrate
- Candidates undergo technical assessments to evaluate their skills
- Depth in Web Project Management
How to prepare
- Answer aloud and timed: Describe a challenging technical problem you faced and how you resolved it.
- Answer aloud and timed: How do you ensure the quality and performance of your code?
Behavioral Interview
reportedA discussion focused on your past experiences and cultural fit.
What to demonstrate
- A discussion focused on your past experiences and cultural fit
- Depth in Web Project Management
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.
Collaborative Discussions
reportedEngagement with potential team members to assess collaboration skills.
What to demonstrate
- Engagement with potential team members to assess collaboration skills
- Depth in Web Project Management
How to prepare
- Answer aloud and timed: What considerations do you take into account when scaling a web application?
- Answer aloud and timed: Describe how you would handle a sudden increase in user traffic on a website.
Final Interview
reportedA concluding interview that may involve various stakeholders.
What to demonstrate
- A concluding interview that may involve various stakeholders
- Depth in Web Project Management
How to prepare
- Answer aloud and timed: How do you approach integrating third-party services into your applications?
- Answer aloud and timed: Describe a time when you had to work with a difficult team member. How did you handle it?
PracHub editorial advice for the preparation topics above.
Prepare for collaboration
Emphasize your teamwork experiences during interviews. Be ready to discuss how you’ve worked with cross-functional teams in the past and how you approach collaboration.
Communicate clearly
Practice articulating your thought process when solving problems. Clear communication of technical concepts is crucial at The Lab.
Know the tools
Familiarity with project management tools and collaboration platforms will be beneficial. Be prepared to discuss how you’ve used these in past projects.
Show your passion
Demonstrate your enthusiasm for technology and continuous learning. Highlight any recent projects or technologies you’ve explored independently.
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 search algorithm for a large dataset?
How would you implement a search algorithm for a large dataset?
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?
Can you explain the time complexity of your solution?
Can you explain the time complexity of your solution?
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?
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?
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 proficient in, and why?
What programming languages are you most proficient in, 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?
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?
How do you ensure the quality and performance of your code?
How do you ensure the quality and performance of your code?
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 and technologies do you prefer for version control and why?
What tools and technologies do you prefer 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 an e-commerce platform from scratch?
How would you design an e-commerce platform from scratch?
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?
What considerations do you take into account when scaling a web application?
What considerations do you take into account when scaling a web application?
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?
Describe how you would handle a sudden increase in user traffic on a website.
Describe how you would handle a sudden increase in user traffic on a website.
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?
How do you approach integrating third-party services into your applications?
How do you approach integrating third-party services into your applications?
Approach
- Say who the caller is and what they do when the call fails halfway.
- Define the identity of a request so a retry cannot double-apply it.
- Separate accepted, pending, failed and confirmed; they are different facts.
- Design the error taxonomy before the success shape; callers branch on it.
Follow-up
- What happens if the caller retries after a timeout?
- How does a client discover it is on an old version of this contract?
How would you approach a project with unclear requirements?
How would you approach a project with unclear requirements?
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?
If a project is falling behind schedule, what steps would you take to get it back on track?
If a project is falling behind schedule, what steps would you take to get it back on track?
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?
Every query on one table stalls for forty seconds mid-deploy
During a release on PostgreSQL, every query touching resource times out for about 40 seconds and then recovers with no intervention. The release ran one migration, ALTER TABLE resource ADD COLUMN archived_reason TEXT, and the migration log shows it completing in 6 ms. Unrelated tables showed no change in error rate. Explain how a 6 ms statement caused a 40-second stall, give the ordered checks you would run on a live system to confirm it, and give the migration procedure that prevents a repeat.
Approach
- Separate the statement's duration from the lock's duration. ADD COLUMN with no default is a catalogue-only change and genuinely runs in milliseconds, but it requires ACCESS EXCLUSIVE, and it cannot acquire that until every transaction already touching the table has finished.
- Account for the queueing, which is the part that surprises people. A lock request that is waiting blocks later requests for conflicting modes behind it rather than letting them overtake, so one long-open transaction holds the DDL and the DDL holds all the traffic. The stall length is set by the longest open transaction, not by the size of the change.
- Confirm on a live system in this order: pg_stat_activity for that table ordered by xact_start, looking for the oldest transaction and specifically for state = idle in transaction; then pg_locks where granted = false to find the waiter; then join them on pid to name blocker and blocked. pg_blocking_pids() does that join for you and is the fastest single call.
- Prevent rather than merely time it better. Set lock_timeout to a second or two on the migration session so the DDL abandons the queue after a bounded wait and is retried, instead of holding it for as long as the oldest transaction lives. Be exact about what that buys: queries arriving during the wait still queue behind the pending ACCESS EXCLUSIVE request, so each attempt costs them up to one lock_timeout of added latency. The outage goes from 40 seconds to about one second per attempt, not to zero. Also run migrations away from deploy-time peaks, and put a statement timeout and an idle-in-transaction timeout on the analytics role that opens the long transactions.
Follow-up
- The same release also wants NOT NULL on that column. What is the sequence that gets there without a long lock?
- Your lock_timeout retry fails ten times in a row because the analytics transaction is always open. What do you change?
Built from the rounds and topics The Lab candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the The Lab loop
- Write out the reported sequence: Initial Screening, Technical Assessment, Behavioral Interview, Collaborative Discussions, Final 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 5 reported rounds, with the weakest marked.
02Work Web Project Management
- Spend the session on Web Project Management, which The Lab candidates report being tested on.
- Write one worked example in Web Project Management and time yourself on it.
Deliverable: One timed worked example in Web Project Management.
03Work E-commerce Platforms & Flows
- Spend the session on E-commerce Platforms & Flows, which The Lab candidates report being tested on.
- Write one worked example in E-commerce Platforms & Flows and time yourself on it.
Deliverable: One timed worked example in E-commerce Platforms & Flows.
04Work Cross-Functional Collaboration
- Spend the session on Cross-Functional Collaboration, which The Lab candidates report being tested on.
- Write one worked example in Cross-Functional Collaboration and time yourself on it.
Deliverable: One timed worked example in Cross-Functional Collaboration.
05Answer out loud: Technical / Domain Questions
- Answer aloud, timed: What programming languages are you most proficient in, and why?
- Answer aloud, timed: Can you explain the software development life cycle and your experience with it?
Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.
06Answer out loud: System Design / Architecture
- Answer aloud, timed: How would you design an e-commerce platform from scratch?
- Answer aloud, timed: What considerations do you take into account when scaling a web application?
Deliverable: Spoken answers to 2 reported System Design / Architecture question(s), under time.
07Answer out loud: Behavioral / Leadership
- Answer aloud, timed: Describe a time when you had to work with a difficult team member. How did you handle it?
- Answer aloud, timed: How do you prioritize tasks when managing multiple projects?
Deliverable: Spoken answers to 2 reported Behavioral / Leadership 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.
Can you explain the software development life cycle and your experience with it?
Can you explain the software development life cycle and your experience with 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?
Describe a time when you had to work with a difficult team member. How did you handle it?
Describe a time when you had to work with a difficult team member. How did you handle 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?
How do you prioritize tasks when managing multiple projects?
How do you prioritize tasks when managing multiple projects?
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?
Can you give an example of how you contributed to a team’s success?
Can you give an example of how you contributed to a team’s success?
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 strategies do you use to communicate complex technical concepts to non-technical stakeholders?
What strategies do you use to communicate complex technical concepts to non-technical stakeholders?
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 time when you had to pivot your approach midway through a project. What did you learn?
Describe a time when you had to pivot your approach midway through a project. What did you learn?
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
Can you explain the software development life cycle and your experience with it?
- 02
Describe a time when you had to work with a difficult team member. How did you handle it?
- 03
How do you prioritize tasks when managing multiple projects?
- 04
Can you give an example of how you contributed to a team’s success?
How difficult are the interviews, and how much preparation time is typically needed?
The interviews can be challenging, particularly the technical assessments. Candidates often find that spending 2-4 weeks preparing thoroughly helps them feel confident and ready. Focus on brushing up on your technical skills and understanding the collaborative nature of the role.
The Lab Software Engineer candidate reports ↗What differentiates successful candidates at The Lab?
Successful candidates often showcase a balance of technical proficiency and strong interpersonal skills. They demonstrate their ability to work collaboratively within a team while also being able to tackle complex technical challenges independently.
The Lab Software Engineer candidate reports ↗What is the company culture like at The Lab?
The culture at The Lab is one of creativity, collaboration, and a no-ego mentality. We value diverse perspectives and encourage open communication among team members to foster innovation.
The Lab Software Engineer candidate reports ↗What is the typical timeline from initial screening to offer?
The timeline can vary, but candidates typically experience a turnaround of 2-6 weeks from the initial screening interview to receiving an offer. This includes technical assessments and multiple interview stages.
The Lab Software Engineer candidate reports ↗What are the hybrid work expectations?
The role is hybrid, with expectations to work in the office Tuesday through Thursday. This balance allows for collaborative work while still providing the flexibility of remote work.
The Lab Software Engineer candidate reports ↗What topics does The Lab test in interviews?
The Lab interviews most often cover Web Project Management, E-commerce Platforms & Flows, Cross-Functional Collaboration, Requirements Translation (Business to Tasks), and Timeline & Resource Planning. The exact emphasis depends on the specific role you apply for.
The Lab 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.
- 01The Lab 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
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