Brex builds corporate cards, expense management and business banking. Its interviews combine practical coding with design questions about payments and ledgers, where correctness is the whole game. This page covers what Brex builds and who it hires, the process candidates commonly report, the technical depth the teams care about, representative problem types, what interviewers score, and a three-week prep plan.
What Brex builds and who it hires
Brex's engineers build card issuing and payments, expense and travel products, accounting integrations and the platform underneath. Brex has written publicly about its back-end evolution, including work in Elixir and Kotlin.
- Back-end engineers: payments, ledgers and integrations.
- Full-stack engineers: product features.
- Infrastructure engineers: platform and reliability.
- Data engineers: reporting and risk.
What the process tends to look like
| Stage | What happens | How to prepare |
|---|---|---|
| Recruiter call | Role, team, level and timeline | Know the product and the team's area |
| Technical screen | A practical coding exercise or data structures problem | Practical coding in your interview language, explained aloud |
| Final loop | Coding, system design focused on payments or data, and behavioral interviews | One design in the company's domain and two strong behavioral stories |
Processes differ by team, level and office and change over time, so treat this as the common shape candidates report and confirm the specifics with your recruiter.
Payments, ledgers and practical code
Ledgers. Expect double-entry thinking: every money movement is recorded as balanced entries, and balances are derived, not overwritten.
Idempotency and retries. Card networks and banks retry and time out. Explain how idempotency keys and state machines prevent duplicate charges.
Practical code quality. Readable, tested code that handles errors is valued over clever one-liners.
Representative problem types
These are the kinds of problems candidates describe, not a leaked question list. Practice the category, not the exact question.
- Design a double-entry ledger for card transactions.
- Handle authorization, capture and refund states.
- Detect duplicate transactions from a card network feed.
- Design spend limits that apply in real time.
- Build a small service with tests and error handling.
- Reconcile internal records with a bank statement.
- Medium algorithm problems.
What interviewers score
- Working code: a solution that runs, handles edge cases and is readable by the next engineer.
- Practical judgment: the trade-offs you name and the simplest design that meets the requirement.
- Product sense: understanding who the user is and what failure looks like for them.
- Ownership: examples where you shipped, measured and fixed things yourself.
The behavioral side
Technical rounds decide most outcomes, but every Brex loop also asks about how you work. Prepare a short story for each of these, with a result and what you learned:
- Something you shipped end to end. Cover the user problem, your decisions, what you measured and what you would change.
- A disagreement with a teammate. Show how you made the decision on evidence and kept the relationship.
- Why this company? Connect its product and engineering problems to the work you want to do next.
Structures and sample answers for the common questions are in our software engineer behavioral answers guide.
A three-week prep plan
- Week 1: practical coding: build small features against an API, parse and transform data, and write tests, in the language you will interview in.
- Week 2: system design for the company's domain, plus two behavioral stories about shipping and fixing something under pressure.
- Week 3: timed mixed problems, a mock interview every other day, and research into the product and its engineering blog.
For practice lists, use LeetCode company-tagged questions and the NeetCode 150 roadmap; for design rounds, read system design building blocks; and compare the practical style of Stripe.
Where CoPilot Interview fits
Most of a Brex loop is spoken: you explain an approach, defend a trade-off and talk through your past work. CoPilot Interview is an AI interview assistant whose free AI mock interview builds technical and behavioral questions from your résumé and the job description, reads them aloud and scores each spoken answer out of ten, so you can rehearse the explanation as well as the code. The free plan gives 15 minutes a day of live help in sessions of up to 15 minutes, with AI mock interviews included. Online assessments and many coding rounds forbid outside help, so practice beforehand and follow your employer's rules on the day.
Disclosure: CoPilot Interview is our product, so weigh what we say about it accordingly.
Frequently asked questions
What programming language should I use in a Brex interview?
Use your strongest mainstream language; Brex's systems include Kotlin and Elixir, but interviews usually allow a choice.
Does Brex send an online assessment?
Candidates mostly describe live technical screens; a separate assessment depends on the role. Ask your recruiter.
How should I prepare for Brex coding questions?
Practice practical problems under time limits, build small features against an API in your interview language, and prepare one system design in Brex's domain. Explain every solution out loud, because follow-up questions about trade-offs matter as much as the first answer.
Can I use AI tools in a Brex interview?
Only if the instructions you receive say so. Online assessments and live coding rounds generally forbid outside help, and some companies now state their AI policy in the invitation. Use AI to practice beforehand, and follow your employer's rules.
Practice this interview before the real one
The AI mock interview builds questions from your resume and the job description, reads them aloud and scores each spoken answer out of 10. Included on the free plan.
Start a mock interview