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Brex System Design Interview: Complete Preparation Guide

Prepare for Brex's system design interview with insights on corporate card platforms, expense management, and financial infrastructure design.

22 minUpdated Apr 25, 2026
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Interview format

5 rounds total.

System Design50 min

Design a corporate financial system. Emphasis on multi-entity accounting, authorization policies, and real-time spend management.

Coding 145 min

Algorithmic problem. Brex uses a mix of Elixir, Go, TypeScript, and Kotlin — language choice is typically flexible.

Coding 245 min

Second coding round, often involving a practical scenario like implementing business logic for financial policies.

Architecture Discussion50 min

Deep dive into system architecture, often focused on event-driven systems, data pipelines, or distributed transaction processing.

Behavioral / Culture45 min

Assesses alignment with Brex values: customer love, craft, speed, and ownership. Expect questions about working in fast-paced startup environments.

Commonly asked systems

Design a corporate card transaction authorization systemDesign a real-time expense management and policy engineDesign a multi-entity corporate accounting systemDesign a receipt matching and categorization pipelineDesign a corporate spend analytics dashboard backendDesign a virtual card issuance and management systemDesign a reimbursement and approval workflow systemDesign a real-time budget tracking system with alerts

What they evaluate

Financial System DesignHigh

Can you design correct, auditable financial systems? Brex evaluates your understanding of ledgers, authorization, and accounting principles.

Policy & Rules Engine DesignHigh

Corporate spend has complex policies. Can you design flexible, configurable rule engines that support diverse business requirements?

Engineering CraftHigh

Brex values high-quality engineering. They evaluate code quality, system elegance, and attention to operational excellence.

Scalability & PerformanceMedium-High

Can you design systems that handle thousands of concurrent card authorizations with low latency?

Product SenseMedium

Brex builds for business users. Can you think about how your system design impacts the user experience for finance teams?

Tips

  • ▸Understand the corporate card ecosystem: card networks, issuer authorization, merchant category codes, and interchange
  • ▸Study policy engine design — Brex's spend management requires complex, configurable rules for approvals and limits
  • ▸Know multi-entity accounting: parent-subsidiary relationships, inter-company transfers, and consolidated reporting
  • ▸Brex uses event-driven architecture extensively — be comfortable with Kafka, event sourcing, and CQRS patterns
  • ▸Think about how real-time authorization decisions work: a card swipe needs approval in under 2 seconds
  • ▸Study receipt matching with ML/OCR — how to extract merchant, amount, and date from receipt images
  • ▸Brex values engineering craft — emphasize clean architecture, good abstractions, and operational considerations

Preparation roadmap

Week 1-2Corporate Finance Fundamentals
  • ·Study the corporate card authorization flow from swipe to settlement
  • ·Learn about expense management: policies, approvals, reimbursements
  • ·Review multi-entity accounting and chart of accounts concepts
  • ·Understand card network economics: interchange, acquiring, issuing
Week 3-4Core Corporate Systems
  • ·Design a real-time card authorization system with policy checks
  • ·Design a configurable expense policy engine
  • ·Design a receipt processing pipeline with OCR and categorization
  • ·Study event-driven architectures: Kafka, event sourcing, CQRS
Week 5-6Advanced Design
  • ·Design a multi-entity corporate accounting ledger
  • ·Design a real-time budget tracking and alerting system
  • ·Design a virtual card issuance platform
  • ·Study operational excellence: monitoring, alerting, runbooks
Week 7-8Mock Interviews & Review
  • ·Do at least 3 mock system design interviews on corporate finance systems
  • ·Practice designing policy engines — these are common at Brex
  • ·Prepare stories about building high-quality software in fast-paced environments
  • ·Review Brex's engineering blog for architecture insights
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