Plaid Senior Software Engineer Interview Questions

1.Tell me about a time when you had to support a teammate who was struggling with their performance or personal challenges. How did you approach the situation and what was the outcome?

2.Give me an example of when you had to give difficult feedback to a peer during a code review or technical discussion. What was the feedback and how did you deliver it?

3.Walk me through a project where you shipped a minimum viable version quickly, then had to iterate based on user feedback. What were the initial shortcuts you took and how did you evolve the solution?

4.Tell me about a time when you discovered a potential security vulnerability or data handling issue in your codebase. How did you handle it and what was the team's reaction?

5.Describe a situation where you had to choose between shipping a feature on time and implementing additional security or reliability measures. How did you make that decision and handle any pushback?

6.Walk me through a recent project where you had to make significant architectural decisions under tight time pressure. How did you gather input and what compromises did you make?

7.You're implementing OAuth 2.0 token refresh logic for Plaid Link. A user's bank session expires mid-transaction and you need to handle the refresh transparently. Walk me through your approach and error handling strategy.

8.Implement rate limiting for Plaid's Auth API that handles different limits per customer tier while maintaining sub-10ms response times. The system needs to handle 100k+ requests per second during peak hours.

9.Our Transactions API is seeing inconsistent categorization accuracy across different banks. Some transactions from Chase are categorized as 'Food & Dining' while identical descriptions from Wells Fargo get 'General Merchandise'. How would you debug and fix this?

10.Code a function that takes a list of bank transactions and returns suspicious patterns that might indicate account takeover fraud. Consider transaction timing, amounts, and merchant patterns.

11.Design the database schema and API endpoints for storing and retrieving identity verification results. This needs to support document verification, biometric matching, and database checks while maintaining audit trails for compliance.

12.Our microservices architecture uses Kafka for event streaming between services. Design a solution for handling out-of-order message delivery when processing bank account updates that affect user balances.

13.Design a circuit breaker system for Plaid's Auth API that prevents cascading failures when a major bank like Chase goes down. We serve 100k+ auth requests per second across 12,000+ financial institutions.

14.Design the caching architecture for Plaid Identity Verification that needs to store document images, biometric templates, and verification results while meeting SOC 2 compliance and supporting instant re-verification requests.

15.Walk me through designing the backend architecture for Plaid Protect's real-time fraud scoring. Every Auth API call needs a fraud score computed in under 50ms using signals from our network of 8,000+ apps.

16.Design the data pipeline that powers Plaid's Transactions API categorization engine. We process 500M+ transactions daily from 12,000+ banks, each with different data formats and categorization needs.

17.Design the token management system for Plaid Link that handles OAuth refresh tokens across 12,000+ banks while ensuring users never see authentication errors during critical financial flows.

18.Design the event-driven architecture that keeps transaction data consistent across Plaid's microservices when a bank account gets closed or frozen. This affects Auth, Balance, Transactions, and Protect APIs simultaneously.

19.Tell me about a time when you had to convince another engineering team to adopt a technical approach or standard that would benefit the broader platform. What resistance did you face and how did you handle it?

20.Describe a situation where you had to step up and lead when your team lead or manager wasn't available during a critical incident or deadline. What decisions did you make and how did you keep the team aligned?

21.Tell me about a time when you identified that your team's development practices were slowing you down or creating quality issues. How did you go about changing them?

22.Walk me through a time when you had to mentor a junior engineer who was making technical decisions that concerned you about security or reliability. How did you approach the coaching conversation?

23.Describe a situation where you disagreed with a technical decision made by leadership or another senior engineer. How did you handle the disagreement and what was the outcome?

24.Tell me about a project where you had to coordinate technical work across multiple teams with competing priorities. How did you align everyone toward a common goal?

25.Plaid Link suddenly starts failing for 20% of users at Chase, but other banks are fine. Walk me through how you'd debug this systematically.

26.Estimate how many API calls per second Plaid's Auth API needs to handle during tax season. Walk me through your assumptions.

27.Our Transactions API categorization accuracy dropped from 92% to 88% last month, but we haven't shipped any ML model updates. How would you investigate what's causing this drift?

28.A major fintech customer wants to migrate 10M users from a competitor to Plaid Auth within 3 months. Estimate the infrastructure costs and engineering effort needed.

29.Plaid Protect's fraud detection is flagging 15% more legitimate transactions as suspicious after a model update. This is blocking real users from connecting accounts. How would you approach fixing this while maintaining fraud prevention effectiveness?

30.A bank integration suddenly starts returning account balances that are $0.01 off from the actual amounts for 30% of users. The bank says their API is working correctly. How would you investigate and decide whether to ship a fix?