Phone ScreenBackend

Technical Phone Screen — Backend

Assess backend skills: API design, databases, concurrency, and system thinking.

Evaluation Criteria

API Design & REST/GraphQL

Evaluates ability to design clean, consistent APIs and understanding of API design principles.

1
2
3
4
5
Sample Questions
  • How do you design a RESTful API for a resource with complex relationships?
  • When would you choose GraphQL over REST, and what are the trade-offs?
  • How do you handle API versioning and backward compatibility?
Strong Signal

Candidate demonstrates clear understanding of resource modeling, HTTP semantics, idempotency, and pagination. They discuss real trade-offs rather than stating one approach is always better.

Weak Signal

Candidate cannot explain REST constraints beyond 'use GET and POST', confuses HTTP status codes, or has no strategy for API evolution and versioning.

Database Design & Query Optimization

Assesses knowledge of data modeling, indexing strategies, and query performance tuning.

1
2
3
4
5
Sample Questions
  • How do you decide between a SQL and NoSQL database for a new project?
  • Walk me through how you'd design the schema for an e-commerce order system.
  • How do you identify and fix slow database queries?
Strong Signal

Candidate discusses normalization trade-offs, indexing strategies with specifics (composite indexes, covering indexes), and uses EXPLAIN plans. They can reason about when denormalization is appropriate.

Weak Signal

Candidate cannot explain indexing beyond 'it makes things faster', has no strategy for schema design, or has never profiled a slow query.

Concurrency & Distributed Systems Basics

Evaluates understanding of concurrency patterns, race conditions, and basic distributed systems concepts.

1
2
3
4
5
Sample Questions
  • How do you handle concurrent writes to the same resource?
  • What is a race condition, and how have you dealt with one?
  • Explain the difference between optimistic and pessimistic locking.
Strong Signal

Candidate explains locking mechanisms, transaction isolation levels, or queue-based approaches with concrete examples. They understand the trade-offs between consistency and availability.

Weak Signal

Candidate has never considered concurrency, confuses threads and processes, or cannot describe a situation where data consistency was a concern.

Error Handling & Observability

Assesses approach to building resilient services with proper error handling, logging, and monitoring.

1
2
3
4
5
Sample Questions
  • How do you design error handling in a backend service?
  • What's your approach to logging and monitoring in production?
  • Describe how you'd debug an intermittent production issue.
Strong Signal

Candidate describes structured logging, correlation IDs, health checks, and alerting strategies. They have a systematic debugging approach and understand the difference between errors, warnings, and info logs.

Weak Signal

Candidate relies on console.log for debugging, has no monitoring strategy, or cannot describe how they would investigate a production incident.

Security Fundamentals

Evaluates awareness of common backend security concerns and secure coding practices.

1
2
3
4
5
Sample Questions
  • What are the most common security vulnerabilities you guard against in backend code?
  • How do you handle authentication and authorization in your services?
  • How do you manage secrets and sensitive configuration?
Strong Signal

Candidate identifies OWASP Top 10 concerns naturally (SQL injection, XSS, CSRF), explains JWT vs. session-based auth trade-offs, and has a strategy for secrets management (vault, env vars, never in code).

Weak Signal

Candidate has never thought about SQL injection, stores passwords in plain text, or commits secrets to version control without concern.

Red Flags to Watch For

  • Cannot explain the difference between SQL and NoSQL at a conceptual level
  • No awareness of authentication/authorization patterns despite claiming backend experience
  • Dismisses testing and monitoring as 'DevOps responsibilities'

Notes & Overall Recommendation

Interview notes go here...

Overall Recommendation:
Strong HireHireNo HireStrong No Hire