SAPI is a library for creating APIs with C#. It's simple by design and allows for a lot of flexibility.
Add as dependency in NuGet
Install-Package SAPI -ProjectName <project>In your preferred IDE: 
By downloading and referencing the DLL (and its dependencies) in your project.
For detailed explanation You can also see docs
// Program.cs using SAPI; using SAPI.Endpoints; using Project.Endpoints; public static void Main(string[] args) { // Init SAPI Server sapi = new(); sapi.Start(); }// Endpoints/Ping.cs using System.Net; using SAPI; namespace Project.Endpoints { public class Ping : Endpoint { public override string url { get; } = "ping"; private override void Get(ref Packet packet) { Console.WriteLine("Ping!"); Error.Page(HttpStatus.EnhanceYourCalm, ref packet); } } }