Plaid Software Engineer Interview Questions

1.Tell me about a time when you noticed a teammate was struggling with their workload or having a tough time personally. How did you step in to help?

2.Tell me about a time you had to make a quick technical decision with incomplete information, then adjust course as you learned more. What was the context?

3.Walk me through a time you shipped something knowing it wasn't perfect, then had to iterate quickly based on user feedback. What drove the decision to ship early?

4.Tell me about a time you had to advocate for a more secure or conservative technical approach when others wanted to move faster. What was at stake?

5.Describe a time when your team was under pressure to ship quickly, but you identified a security or reliability risk. How did you handle the tradeoff?

6.Walk me through the hardest interpersonal conflict you've had with a teammate in the last year. What was the disagreement and how did you work through it?

7.Implement a function that takes a list of bank transactions and returns the most common spending category for each month. Handle edge cases and optimize for readability.

8.You're debugging a production issue where Plaid Link is failing to connect for users of a specific bank, but the bank's API status page shows everything is green. Walk me through your investigation approach and what you'd check first.

9.You're implementing a new API endpoint for the Transactions service that needs to handle 50,000 requests per minute. The endpoint fetches categorized transaction data from multiple bank connections and needs to respond within 100ms P95. How would you design this?

10.A fraud pattern is detected in Plaid Protect where attackers are making rapid account connection attempts from the same IP ranges. You need to implement rate limiting that doesn't block legitimate users. Code up the core rate limiting logic.

11.Design the database schema and API contract for a new feature that lets users see which apps have access to their bank accounts, when they last accessed data, and revoke access. Consider Plaid's multi-tenant architecture and compliance requirements.

12.Design a distributed caching layer for Plaid's Auth API that needs to cache bank account verification results. The cache must handle 100k+ requests per second, maintain data consistency across regions, and support cache invalidation when account details change.

13.Design a monitoring and alerting system for Plaid's Auth API that can detect when individual banks are experiencing issues before customer support tickets arrive.

14.Design a local development environment setup that lets new Plaid engineers run a subset of microservices on their laptops while connecting to shared staging services for bank integrations.

15.Design a webhook delivery system for Plaid's Transactions API that guarantees at least once delivery to fintech partners. Some partners receive 50M+ webhook events per day and have varying reliability.

16.You need to design a configuration service that manages feature flags and API rate limits across all of Plaid's microservices. Changes should propagate to 500+ service instances within 30 seconds without requiring restarts.

17.Design a real-time fraud detection system for Plaid Link that can flag suspicious account connection attempts within 50ms. You need to handle 10,000 Link initializations per minute across thousands of financial institutions.

18.Design the data pipeline for Plaid Identity Verification that needs to process document images, run biometric checks, and query multiple identity databases within 10 seconds for a verification decision.

19.Tell me about a time you had to convince a product manager or designer to change direction on a feature based on technical constraints or security concerns.

20.Describe a time you took ownership of a production issue that wasn't directly caused by your code. How did you coordinate the response?

21.Walk me through a time you had to influence an engineer on another team to prioritize fixing something that was blocking your work, but wasn't urgent for them.

22.Tell me about a time you disagreed with your manager's technical decision but went ahead and implemented it anyway. How did you handle that situation?

23.Describe a time you identified a significant technical debt or architecture issue that would impact multiple teams, but wasn't an immediate priority for leadership. How did you build consensus to address it?

24.Tell me about a time you had to onboard a new team member when you were also dealing with a major deadline or production issue. How did you balance mentoring with delivery pressure?

25.Estimate how many bank connections Plaid processes per day across all our APIs. Walk me through your assumptions and reasoning.

26.A fintech partner reports that Plaid Link success rates dropped from 95% to 87% for their users, but our overall metrics show stable performance. How would you investigate this discrepancy?

27.Plaid's Transactions API response times have increased by 30ms P95 over the past month, but no major features shipped. Estimate the potential revenue impact and walk me through how you'd prioritize investigating this.

28.You need to estimate storage costs for a new feature that will archive transaction data for 7 years to meet compliance requirements. Walk me through your approach and key assumptions.

29.Estimate how much additional compute capacity Plaid would need if we launched in a new country with 50 million bank accounts. What factors would drive your calculations?

30.Plaid wants to reduce the number of customer support tickets related to bank connection failures by 25%. How would you approach this problem and estimate the engineering effort required?