How Should I Prepare for a C# Interview at a Company With Proprietary Software?

Ask the recruiter what format the interview will take. It could involve computer science concepts, live coding in a language you choose, debugging existing code, pair programming, or a data-structures exercise. Knowing the format is much more useful than guessing what the company’s proprietary tools might be like.

The technology list suggests the role may involve maintaining a fairly custom or older system, so ask what “proprietary” actually means in practice. Find out whether the interview focuses on building something new, fixing an existing bug, or understanding their architecture. Some companies use that term for perfectly manageable internal tools, while others have old generated code and limited documentation, which can make the day-to-day work very different.

“Proprietary” usually just means the software was built internally or heavily customized, so they probably aren’t expecting you to know it already. They’re more likely looking for someone who can explore an unfamiliar codebase, make reasonable assumptions, ask good questions, and explain their thinking clearly. Practice reading messy or unfamiliar C# projects and tracing how the pieces fit together.

Since C# is your strongest language, review core .NET and C# concepts, object-oriented design, exception handling, collections, async code, and basic application architecture. It would also be worth reviewing SQL joins, filtering, grouping, and writing queries without relying too heavily on a visual query builder. A little familiarity with deployment practices, DevOps, and service-based architecture could help too.