Your first minimal API

The mental model

A .NET API is just a program that starts a web server, maps HTTP routes to C# functions, and waits for requests. ASP.NET Core’s Minimal APIs let you express that directly in Program.cs.

var app = WebApplication.Create(args);

app.MapGet("/", () => "Hello World!");

app.Run();

Your terminal path

On Linux and macOS, the official path is the dotnet CLI. The CLI comes with the .NET SDK and works the same way across both systems.

• dotnet --info
• mkdir dotnet-api-lab && cd dotnet-api-lab
• dotnet new web -n HelloApi
• cd HelloApi
• dotnet run
• curl http://localhost:5000

If dotnet --info fails, install the .NET SDK first. Prefer the official Microsoft package instructions for your Linux distro or macOS installer/Homebrew route.

Open Program.cs

For a fresh dotnet new web app, expect something close to this:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", () => "Hello World!");

app.Run();

Read it literally: create a builder, build an app, map GET / to a function, run the web server. The lambda () => "Hello World!" is the request handler.

Make it an API, not just hello world

Replace the route with a small JSON response:

app.MapGet("/status", () => new
{
    Service = "HelloApi",
    Status = "ok",
    CheckedAt = DateTimeOffset.UtcNow
});

Then run again and call it:

dotnet run
curl http://localhost:5000/status

If the console says it is listening on a different port, use that port. On modern templates it may choose a random dev port like http://localhost:5123.

Primary source

Read Microsoft Learn’s Minimal APIs overview and .NET CLI overview when you want the official reference:Minimal APIsand .NET CLI.