ASP.NET Core is a web framework—not a language. It runs on the .NET runtime and lets you build sites, APIs, and microservices with C# (or F#). Version 8+ is cross-platform: Linux containers, Windows IIS, and macOS dev machines share the same codebase.
Core characteristics
- Unified stack — MVC, Razor Pages, Web API, minimal APIs, SignalR, and Blazor share the same host and middleware pipeline
- High performance — Kestrel web server and efficient async I/O; used in production at scale with tuning
- Dependency injection built in — services registered in
Program.csand injected into controllers - Configuration everywhere — JSON, environment variables, Azure Key Vault providers
What ASP.NET Core is not
Not a front-end framework (pair with React/Vue/Blazor for rich UIs), not legacy .NET Framework-only (Core is the modern path), and not magic—you still need HTTP, SQL basics, and C# fundamentals.
Important interview questions and answers
- Q: ASP.NET vs ASP.NET Core?
A: Core is cross-platform, modular, and the active development path; legacy ASP.NET ran on Windows IIS with System.Web. - Q: What hosts ASP.NET Core?
A: Kestrel is the default in-process server; reverse proxies (IIS, nginx, Azure Front Door) sit in front in production. - Q: Is C# required?
A: C# is the primary language; F# and VB.NET exist but C# dominates hiring and docs.
Self-check
- Name two app types ASP.NET Core supports (MVC, API, etc.).
- What language is most ASP.NET Core code written in?
Interview prep
- What hosts ASP.NET Core by default?
Kestrel is the default in-process web server; production often places IIS, nginx, or Azure Front Door as a reverse proxy in front of Kestrel.