I had a really great chat with a senior backend interviewer …

I asked him what really matters when he's evaluating candidates.

Here’s the top 5:

1. Programming Language MasteryHe wants candidates to know their primary backend language really well: Python, Java, C#, it doesn't matter.The more senior the position, the more advanced topics like concurrency, memory management, and language-specific features he explores.

2. Database & SQL KnowledgeHe always checks if candidates are comfortable with SQL databases and never asks about a deep understanding of noSQL. Be ready to chat about ACID, query optimization, schema design, and concepts like indexing and transactions.

3. APIs & Web ServicesCandidates should know how to build RESTful APIs, why other options exist (GraphQL), and how to handle authentication. Additional questions about rate limiting, API versioning, and webhooks are possible.

4. System DesignYes, even for junior roles, he asks candidates system architecture questions. You’ll need to explain how to design systems for scalability, fault tolerance, and high availability. Of course, he expects more or less based on the role.

5. SecuritySecurity is non-negotiable and is always asked. He'll ask about SQL injection, XSS, CSRF, and how you secure APIs. If you don't mention data encryption, hashing, input validation, or authentication best practices, that's a red flag.