NSwag

NSwag is a set of tools for .NET developers that automates two related tasks: describing how a web API works, and generating the code needed to call it from other applications.

When you build a web API in .NET or ASP.NET Core (Microsoft's frameworks for building websites and services), NSwag can read your existing code and produce an OpenAPI (formerly called Swagger) specification. This is a standardized document that describes every endpoint your API offers, what inputs each one expects, and what it returns. The document acts as a machine-readable contract that other tools can consume.

From that contract, NSwag generates ready-to-use client code in C# or TypeScript. Instead of writing by hand the code that calls your API from a website or another service, NSwag writes it for you. TypeScript clients are available for several popular frontend frameworks including Angular, AngularJS, React (via the Fetch template), and Aurelia. C# clients can be used in regular .NET apps, .NET Core, and Xamarin for mobile apps.

The toolchain runs several ways: through NSwagStudio, a Windows desktop application with a graphical interface; via a command line tool that works on Windows, Mac, and Linux; directly in C# code via NuGet packages; or as part of an automated build process through MSBuild targets. ASP.NET Core projects can add a middleware layer that serves the generated documentation page and an interactive browser UI alongside the running application, letting developers and consumers of the API explore available endpoints without reading code.