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MSD Software Engineer Interview Guide

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

The 60-second brief

As a Software Engineer at MSD (known as Merck & Co., Inc. in the US and Canada), you play a critical role in building and scaling digital technologies that support global healthcare, biopharmaceutical manufacturing, and clinical research. MSD relies on modern software engineering practices to power core enterprise systems, advance data-driven drug discovery, streamline global supply chain logistics, and deliver robust software solutions across international tech hubs like Prague, Singapore, Rahway, and Hyderabad. In this position, your day-to-day impact reaches far beyond traditional tech platforms. You are tasked with developing resilient back-end services, robust user interfaces, clean API integrations, and scalable data ingestion pipelines.

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

Focus areas

  • Coding tests (online assessments)
  • Technical interview preparation
  • Java

The MSD interview process

MSD candidates report 5 rounds over 4-6 weeks. The stages below are what candidates describe, not a published process.

Recruiter Screening

Short call to review past experience, salary expectations, and position fit.

What to demonstrate

  • Short call to review past experience, salary expectations, and position fit
  • Depth in Coding tests (online assessments)

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.

Online Assessment

Candidates complete an online assessment or practical technical evaluation.

What to demonstrate

  • Candidates complete an online assessment or practical technical evaluation
  • Depth in Coding tests (online assessments)

How to prepare

  • Answer aloud and timed: Explain the key features of the Spring framework and how dependency injection works under the hood.
  • Answer aloud and timed: What is the difference between synchronous and asynchronous request processing in web frameworks like Next.js or Node.js?

Walk-in Assessment/Take-home

In certain regions, candidates may participate in walk-in assessments or complete take-home assignments.

What to demonstrate

  • In certain regions, candidates may participate in walk-in assessments or complete take-home assignments
  • Depth in Coding tests (online assessments)

How to prepare

  • Answer aloud and timed: How do basic operating system principles, such as process management and memory allocation, affect backend service performance?
  • Answer aloud and timed: How would you design a system to handle high-volume data ingestion, such as streaming sensor data from manufacturing plants?

Technical Interviews

Interviews with senior developers focusing on past project work and system design discussions.

What to demonstrate

  • Interviews with senior developers focusing on past project work and system design discussions
  • Depth in Coding tests (online assessments)

How to prepare

  • Answer aloud and timed: How do you scale RESTful endpoints when handling high request volumes across distributed global teams?
  • Answer aloud and timed: Compare relational databases with NoSQL databases; when would you choose one over the other for processing clinical test data?

Panel Discussions

Final discussions with managers and HR to evaluate behavioral scenarios and cultural fit.

What to demonstrate

  • Final discussions with managers and HR to evaluate behavioral scenarios and cultural fit
  • Depth in Coding tests (online assessments)

How to prepare

  • Answer aloud and timed: How would you structure a file ingestion and processing system that supports artificial intelligence and machine learning pipelines?
  • Answer aloud and timed: What trade-offs do you consider when choosing between a monolithic architecture and modern microservices?

Where candidates lose points

Prepare a clear, structured overview of your key past projects

Interviewers frequently anchor technical conversations around systems you have already built, asking you to defend your framework choices and implementation decisions.

Focus on Practical Trade-offs Over Syntax

When answering system design or architecture questions, emphasize trade-offs—such as latency vs. throughput or SQL vs. NoSQL—rather than focusing strictly on code syntax.

Structure Your Behavioral Answers

Use the STAR framework (Situation, Task, Action, Result) for situational questions. Highlight your specific contributions, teamwork, and measurable outcomes.

Questions & practice

What is the difference between synchronous and asynchronous request processing in web frameworks like Next.js

Medium · Core Technical Skills & Programming Fund

What is the difference between synchronous and asynchronous request processing in web frameworks like Next.js or Node.js?

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 basic operating system principles, such as process management and memory allocation, affect backend ser

Medium · Core Technical Skills & Programming Fund

How do basic operating system principles, such as process management and memory allocation, affect backend service performance?

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?

Walk us through creating a Python script and lightweight web server to receive HTTP requests and return custom

Medium · Practical Coding & Practical Problem-Sol

Walk us through creating a Python script and lightweight web server to receive HTTP requests and return custom JSON payloads.

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 optimize slow-performing SQL queries, and what indices would you add to improve search performance?

Medium · Core Technical Skills & Programming Fund

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?

Find version gaps and relay lag with window functions

Medium · window functions · event tables · frame semantics

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

  1. 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.
  2. 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.
  3. 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.
  4. 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 are the core principles of Object-Oriented Programming (OOP), and how do you implement inheritance and en

Medium · Core Technical Skills & Programming Fund

What are the core principles of Object-Oriented Programming (OOP), and how do you implement inheritance and encapsulation in Python or Java?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain the key features of the Spring framework and how dependency injection works under the hood.

Medium · Core Technical Skills & Programming Fund

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. 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 system to handle high-volume data ingestion, such as streaming sensor data from manufac

Medium · System Design & Architectural Trade-offs

How would you design a system to handle high-volume data ingestion, such as streaming sensor data from manufacturing plants?

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 scale RESTful endpoints when handling high request volumes across distributed global teams?

Medium · System Design & Architectural Trade-offs

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?

Compare relational databases with NoSQL databases; when would you choose one over the other for processing cli

Medium · System Design & Architectural Trade-offs

Compare relational databases with NoSQL databases; when would you choose one over the other for processing clinical test data?

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 would you structure a file ingestion and processing system that supports artificial intelligence and machi

Medium · System Design & Architectural Trade-offs

How would you structure a file ingestion and processing system that supports artificial intelligence and machine learning pipelines?

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?

What trade-offs do you consider when choosing between a monolithic architecture and modern microservices?

Medium · System Design & Architectural Trade-offs

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?

Explain the architecture, folder structure, and technical choices of a web application you built during a take

Medium · Practical Coding & Practical Problem-Sol

Explain the architecture, folder structure, and technical choices of a web application you built during a take-home coding assignment.

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 structure unit and integration tests to ensure code quality before pushing to production?

Medium · Practical Coding & Practical Problem-Sol

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. 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 design a data ingestion script to gracefully handle corrupted inputs or network timeouts?

Medium · Practical Coding & Practical Problem-Sol

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?

Describe how you debug a memory leak or unexpected high CPU usage in a production environment.

Medium · Practical Coding & Practical Problem-Sol

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 MSD candidates report.

Day 1 — Map the MSD loop

  • Write out the reported sequence: Recruiter Screening, Online Assessment, Walk-in Assessment/Take-home, Technical Interviews, Panel 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 5 reported rounds, with the weakest marked.

Day 2 — Work Coding tests (online assessments)

  • Spend the session on Coding tests (online assessments), which MSD candidates report being tested on.
  • Write one worked example in Coding tests (online assessments) and time yourself on it.

Deliverable: One timed worked example in Coding tests (online assessments).

Day 3 — Work Technical interview preparation

  • Spend the session on Technical interview preparation, which MSD candidates report being tested on.
  • Write one worked example in Technical interview preparation and time yourself on it.

Deliverable: One timed worked example in Technical interview preparation.

Day 4 — Work Java

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

Deliverable: One timed worked example in Java.

Day 5 — Answer out loud: Core Technical Skills & Programming Fundamentals

  • Answer aloud, timed: What are the core principles of Object-Oriented Programming (OOP), and how do you implement inheritance and encapsulation in Python or Java?
  • Answer aloud, timed: How do you optimize slow-performing SQL queries, and what indices would you add to improve search performance?

Deliverable: Spoken answers to 2 reported Core Technical Skills & Programming Fundamentals question(s), under time.

Day 6 — Answer out loud: System Design & Architectural Trade-offs

  • Answer aloud, timed: How would you design a system to handle high-volume data ingestion, such as streaming sensor data from manufacturing plants?
  • Answer aloud, timed: How do you scale RESTful endpoints when handling high request volumes across distributed global teams?

Deliverable: Spoken answers to 2 reported System Design & Architectural Trade-offs question(s), under time.

Day 7 — Answer out loud: Practical Coding & Practical Problem-Solving

  • Answer aloud, timed: Explain the architecture, folder structure, and technical choices of a web application you built during a take-home coding assignment.
  • Answer aloud, timed: Walk us through creating a Python script and lightweight web server to receive HTTP requests and return custom JSON payloads.

Deliverable: Spoken answers to 2 reported Practical Coding & Practical Problem-Solving question(s), under time.

Behavioural preparation

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

Tell me about a time when you were a dominant or leading team member on a project. How did you ensure collabor

Medium · Behavioral & Situational Leadership

Tell me about a time when you were a dominant or leading team member on a project. How did you ensure collaboration and alignment?

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 manage your time and prioritize tasks when faced with competing deadlines from multiple business un

Medium · Behavioral & Situational Leadership

How do you manage your time and prioritize tasks when faced with competing deadlines from multiple business units?

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 scenario where you disagreed with a senior engineer or team lead on an architectural decision. How

Medium · Behavioral & Situational Leadership

Describe a scenario where you disagreed with a senior engineer or team lead on an architectural decision. How was it resolved?

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 explain complex technical concepts to non-technical stakeholders, such as clinical leads or product

Medium · Behavioral & Situational Leadership

How do you explain complex technical concepts to non-technical stakeholders, such as clinical leads or product managers?

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?

Tell me about a project that did not go according to plan. What went wrong, and what did you learn from the ex

Medium · Behavioral & Situational Leadership

Tell me about a project that did not go according to plan. What went wrong, and what did you learn from the 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?