Brex Engineering Manager Interview Questions

1.Tell me about a cross-team problem you identified that nobody explicitly asked you to fix. How did you decide to own it, and what did you actually do?

2.Tell me about a written doc — a design doc, a proposal, an RFC — that you authored that actually changed the direction of your team or org. What was in it, and what shifted?

3.Walk me through a time you chose to invest in a harder, more correct solution instead of the quick fix. What was the pressure to take the shortcut, and what did you have to give up to do it right?

4.Tell me about a time you had to share information with your team or stakeholders that was genuinely uncomfortable — bad news about a project, an honest assessment of someone's performance, or a mistake you made. What did you share, how did you share it, and what happened?

5.Tell me about a time an incident or major failure in your team's system happened and the root cause pointed back to something you had de-prioritized or a call you made. How did you handle it with your team, with leadership, and with the affected customers?

6.Tell me about a time you wrote a doc that proposed a significant architectural or process change and had to get people to move from disagreement to alignment. What was the resistance, and how did the doc itself do the work of changing minds?

7.Your team owns a Kafka consumer that processes Brex Card authorization events. A deploy goes out and the consumer lag starts climbing — it's now 10 minutes behind real-time. What's your first move, and how do you think about the tradeoffs involved in catching up?

8.You're an EM on the Brex Spend Management team. A senior IC on your team insists on rewriting a critical expense categorization service from TypeScript to Elixir, arguing it'll make the code more correct and maintainable. How do you evaluate that proposal?

9.We need to build a reimbursements feature in Brex Spend Management where an employee submits an out-of-pocket expense, it gets approved by a manager, and funds get pushed to their bank account. Walk me through how you'd design the state machine and the persistence model for this workflow.

10.Your team's gRPC service handles real-time spend policy evaluation for Brex Card — every card swipe goes through it. P99 latency has been creeping up over the past two weeks but there's been no deploy. What's your diagnostic approach, and what architectural levers would you consider pulling?

11.You're designing the ledger for Brex Business Account — a banking product that holds real customer operating cash. What's your data model for ensuring ledger correctness at scale, and how do you handle the consistency boundary between your internal ledger and the external banking partner's records?

12.You're leading engineering for Brex Empower and need to migrate a high-traffic multi-tenant PostgreSQL database to a sharded model because single-instance write throughput is the bottleneck. You can't take downtime. Walk me through your migration strategy.

13.Design a rate-limiting system for Brex Card's authorization API. Every card swipe globally hits this path, and a single enterprise customer might have tens of thousands of cards active simultaneously.

14.Walk me through how you'd design an idempotency layer for Brex's bill pay API. Finance teams are submitting vendor payments, and we need to guarantee that a network retry never results in a duplicate wire transfer.

15.Design the multi-currency transaction normalization pipeline for Brex Empower. Enterprise customers transact in 30+ currencies, and finance teams need to report consolidated spend in their home currency with accurate FX rates pinned at transaction time.

16.Design Brex's real-time spend policy engine — the service that evaluates whether a given card transaction should be approved or declined based on rules a company's admin has configured, like 'no alcohol purchases' or '$500 limit per transaction for software engineers'.

17.Design a global duplicate transaction detection system for Brex Card. We process millions of authorizations per day across hundreds of acquiring banks, and we need to catch cases where the same charge hits our system twice — within milliseconds and across a 72-hour window for delayed settlement.

18.Design Brex's spend analytics pipeline — the system that powers real-time spend dashboards in Brex Spend Management. Finance teams expect to see live card spend aggregated by department, category, and employee within seconds of a transaction, while also running month-end reports over billions of historical rows.

19.Tell me about a time you had to onboard an engineer into a new codebase or system quickly. What did you do to accelerate their ramp, and how did you measure whether it worked?

20.Describe how you've built or maintained a strong engineering hiring bar on your team. What does a 'good hire' look like to you, and how have you operationalized that standard?

21.Tell me about the most junior engineer you've taken from underperforming to genuinely high-performing. What did you diagnose, what did you change, and how long did it take?

22.Tell me about a time you had to push back on a product or business stakeholder who wanted to ship something faster than you believed was safe or correct. How did you frame your position, and what was the outcome?

23.You're six months into leading a team and you realize your team's technical strategy is misaligned with where two adjacent teams are heading architecturally — but no one has flagged it yet. What do you do?

24.Tell me about a time you had to make a significant resourcing or organizational structure change to your team — splitting a team, merging it with another, or fundamentally reshuffling ownership — and the decision was contested. How did you navigate it?

25.Roughly how many Brex Card transactions do you think we process on a typical weekday, and what does that imply about the infrastructure footprint needed to support real-time authorization?

26.Activation rate for new Brex Spend Management customers dropped 8% month-over-month. Finance teams aren't completing expense policy setup within their first 30 days. How do you think about diagnosing this, and what would you prioritize investigating first?

27.Estimate the annual dollar value of fraudulent transactions that Brex's fraud detection system needs to catch or prevent across the Brex Card portfolio. Walk me through your assumptions and what this implies for how you'd staff and prioritize a fraud engineering team.

28.Your team owns the expense reporting flow in Brex Spend Management. You're told that average time-to-reimbursement for employees has increased from 3 days to 7 days over the past quarter, but no engineering changes shipped. How do you structure your investigation, and what's your null hypothesis?

29.Brex is considering launching a new feature that lets enterprise finance teams set dynamic per-employee spend limits that automatically adjust based on the employee's seniority tier and department budget remaining. Estimate the engineering complexity and size the team you'd need to ship an MVP in one quarter.

30.Brex is evaluating whether to build a native travel booking experience directly in the Brex Spend Management platform versus continuing to integrate with third-party travel tools. What analytical framework would you use to make that build-vs-partner decision, and what data would you want before making a recommendation?