Marsh Software Engineer Interview Guide

The 60-second brief

At Marsh, a global leader in insurance brokering and risk management, a Software Engineer does not just write code; you build the digital foundation that helps organizations navigate systemic global risks. As part of Marsh McLennan, the technology teams are responsible for designing, developing, and maintaining complex enterprise platforms that process massive amounts of risk data, automate insurance placements, and power client-facing portals. Whether you are working on cloud automation, modernizing legacy systems, or developing advanced predictive analytics tools, your work directly impacts the resilience of businesses worldwide. The engineering organization at Marsh operates at an incredible scale, requiring robust system architectures that prioritize security, high availability, and performance.

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

Focus areas

• Ext JS
• Data Structures & Algorithms (DSA)
• System Architecture / System Design (Strategy & Architecture

The Marsh interview process

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

Online Assessment

Candidates begin with an online assessment focusing on aptitude and core computer science concepts.

What to demonstrate

• Candidates begin with an online assessment focusing on aptitude and core computer science concepts
• Depth in Ext JS

How to prepare

• Answer aloud and timed: Explain the four pillars of Object-Oriented Programming (OOPs) and provide real-world examples of how you have applied them.
• Answer aloud and timed: What is the difference between an inner join, left join, and outer join in SQL? Write a query to find duplicate records in a table.

Technical Interviews

Candidates participate in live technical interviews to evaluate their technical depth.

What to demonstrate

• Candidates participate in live technical interviews to evaluate their technical depth
• Depth in Ext JS

How to prepare

• Answer aloud and timed: Explain the concept of database normalization. When would you deliberately choose to denormalize a database?
• Answer aloud and timed: What is the difference between a process and a thread in an Operating System? How does multi-threading work in your primary programming language?

Architectural Evaluations

For senior roles, candidates undergo architectural evaluations to assess their design skills.

What to demonstrate

• For senior roles, candidates undergo architectural evaluations to assess their design skills
• Depth in Ext JS

How to prepare

• Answer aloud and timed: Explain the basics of computer networking, specifically how a TCP/IP handshake works and the difference between HTTP and HTTPS.
• Answer aloud and timed: Write a function to check if a given string or number is a palindrome without using built-in reverse functions.

Managerial and Behavioral Round

Final round focusing on managerial and behavioral aspects to gauge cultural fit.

What to demonstrate

• Final round focusing on managerial and behavioral aspects to gauge cultural fit
• Depth in Ext JS

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 managerial and behavioral round above and write down what you would ask to confirm before it.

Where candidates lose points

Master Your Resume

Be prepared to explain every single project, technology, and bullet point on your resume. Marsh interviewers frequently use your resume as the primary roadmap for technical and situational questions.

Understand the Business Domain

While you are applying for a technical role, showing an understanding of risk management, insurance brokering, or general financial services will set you apart from other candidates.

Communicate Your Thought Process

During coding and system design rounds, do not jump straight to writing code. Talk through your approach, discuss trade-offs, and clarify assumptions with your interviewer first.

Be Patient but Proactive

The hiring process can sometimes feel slow due to the size and compliance requirements of Marsh McLennan. Keep in touch with your recruiter, but expect some latency between rounds.

Questions & practice

What is the difference between a process and a thread in an Operating System? How does multi-threading work in

Medium · Core CS Fundamentals & Databases

What is the difference between a process and a thread in an Operating System? How does multi-threading work in your primary programming language?

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?

Write a function to check if a given string or number is a palindrome without using built-in reverse functions

Medium · Coding & Algorithms

Write a function to check if a given string or number is a palindrome without using built-in reverse functions.

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 convert a decimal number to its binary representation? Write an algorithm to solve this.

Medium · Coding & Algorithms

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 an array of integers, write an efficient algorithm to find the subarray with the largest sum.

Medium · Coding & Algorithms

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?

Explain how a binary search algorithm works. What is its time and space complexity compared to linear search?

Medium · Coding & Algorithms

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?

Solve a string manipulation problem: reverse the words in a given sentence while preserving spaces and special

Medium · Coding & Algorithms

Solve a string manipulation problem: reverse the words in a given sentence while preserving spaces and special characters.

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?

Explain the differences between var, let, and const in modern JavaScript. How does the event loop handle

Medium · Frameworks & Modern Web Technologies

Explain the differences between var, let, and const in modern JavaScript. How does the event loop handle asynchronous code?

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?

What is the difference between an inner join, left join, and outer join in SQL? Write a query to find duplicat

Medium · Core CS Fundamentals & Databases

What is the difference between an inner join, left join, and outer join in SQL? Write a query to find duplicate records in a table.

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 the concept of database normalization. When would you deliberately choose to denormalize a database?

Medium · Core CS Fundamentals & Databases

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 the four pillars of Object-Oriented Programming (OOPs) and provide real-world examples of how you have

Medium · Core CS Fundamentals & Databases

Explain the four pillars of Object-Oriented Programming (OOPs) and provide real-world examples of how you have applied them.

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 basics of computer networking, specifically how a TCP/IP handshake works and the difference betwee

Medium · Core CS Fundamentals & Databases

Explain the basics of computer networking, specifically how a TCP/IP handshake works and the difference between HTTP and HTTPS.

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?

What are the core concepts of ExtJS, and how do you manage state and component lifecycles within an ExtJS appl

Medium · Frameworks & Modern Web Technologies

What are the core concepts of ExtJS, and how do you manage state and component lifecycles within an ExtJS application?

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 do you secure a REST API? Explain the concepts of OAuth2 and JWT tokens.

Medium · Frameworks & Modern Web Technologies

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?

What are microservices, and how do you handle inter-service communication and data consistency across microser

Medium · Frameworks & Modern Web Technologies

What are microservices, and how do you handle inter-service communication and data consistency across microservices?

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?

Every query on one table stalls for forty seconds mid-deploy

Medium · lock contention · ddl · migrations

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

1. 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.
2. 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.
3. 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.
4. 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?

Suggested practice checklist

Built from the rounds and topics Marsh candidates report.

Day 1 — Map the Marsh loop

• Write out the reported sequence: Online Assessment, Technical Interviews, Architectural Evaluations, Managerial and Behavioral Round.
• 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 Ext JS

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

Deliverable: One timed worked example in Ext JS.

Day 3 — Work Data Structures & Algorithms (DSA)

• Spend the session on Data Structures & Algorithms (DSA), which Marsh 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).

Day 4 — Work System Architecture / System Design (Strategy & Architecture Questions)

• Spend the session on System Architecture / System Design (Strategy & Architecture Questions), which Marsh candidates report being tested on.
• Write one worked example in System Architecture / System Design (Strategy & Architecture Questions) and time yourself on it.

Deliverable: One timed worked example in System Architecture / System Design (Strategy & Architecture Questions).

Day 5 — Answer out loud: Core CS Fundamentals & Databases

• Answer aloud, timed: Explain the four pillars of Object-Oriented Programming (OOPs) and provide real-world examples of how you have applied them.
• Answer aloud, timed: What is the difference between an inner join, left join, and outer join in SQL? Write a query to find duplicate records in a table.

Deliverable: Spoken answers to 2 reported Core CS Fundamentals & Databases question(s), under time.

Day 6 — Answer out loud: Coding & Algorithms

• Answer aloud, timed: Write a function to check if a given string or number is a palindrome without using built-in reverse functions.
• Answer aloud, timed: How do you convert a decimal number to its binary representation? Write an algorithm to solve this.

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

Day 7 — Answer out loud: Frameworks & Modern Web Technologies

• Answer aloud, timed: Explain your experience with Spring Boot. How does dependency injection work under the hood?
• Answer aloud, timed: What are the core concepts of ExtJS, and how do you manage state and component lifecycles within an ExtJS application?

Deliverable: Spoken answers to 2 reported Frameworks & Modern Web Technologies question(s), under time.

Behavioural preparation

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

Explain your experience with Spring Boot. How does dependency injection work under the hood?

Medium · Frameworks & Modern Web Technologies

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 time you had to work with a difficult stakeholder or team member. How did you resolve the conf

Medium · Behavioral & Situational

Tell me about a time you had to work with a difficult stakeholder or team member. How did you resolve the conflict?

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 challenging technical project you worked on. What were the roadblocks, and how did you overcome the

Medium · Behavioral & Situational

Describe a challenging technical project you worked on. What were the roadblocks, and how did you overcome them?

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 prioritize your tasks when faced with tight deadlines and competing priorities?

Medium · Behavioral & Situational

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?

Walk me through your resume and explain why you are interested in transitioning to the financial services and

Medium · Behavioral & Situational

Walk me through your resume and explain why you are interested in transitioning to the financial services and risk management sector at Marsh.

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 time you made a mistake on a project. How did you handle it, and what did you learn from the e

Medium · Behavioral & Situational

Tell me about a time you made a mistake on a project. How did you handle it, 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?