CodePath — Learn coding from zero to expert

1. What is this?

A server is a program that waits for requests and sends responses. In ASP.NET Core, a route maps a URL to code: app.MapGet("/", () => "Hello") means 'when someone visits /, reply Hello'. The example below is console C# (runnable here); the web form is shown so you recognise it.

2. Why do we use it?

Login, checkout, feeds — all are requests answered by servers. .NET is a mainstream way to build them reliably.

3. Syntax breakdown

```
Console.WriteLine("Hello from .NET");
```
Prints a line — runnable in this editor to confirm your setup works.
```
app.MapGet("/", () => "Hello");
```
Web form (read-only here): route / replies Hello. () => ... is a small function.
```
app.Run();
```
Starts the server so it listens for requests.

5. Common mistakes

Trying to run app.MapGet in the console runner — it needs a web host; the runnable part here is the Console line.
Forgetting app.Run() so the server never starts.
Confusing the URL path ("/") with the returned text.

Practice task

Change the message to "Hello, <your name>, from .NET" and run.

Hint

Edit the string inside WriteLine.

Try it below — tests run automatically when you press Run.

dotnet

Output

Press Run to see output.

Mini quiz

3 questions. Answer, then check.

1. What is a server?
2. What does app.MapGet("/", ...) do?
3. What starts an ASP.NET Core server?