Best extension to convert C# Class to Typescript Interface Class

Yes there are many plugin available to convert C# class file into typescript some of them are 

1. Typewriter  : looks easy to use, it can create new typescript files when you create a C# class file and save it(after installing it)
2. http://type.litesolutions.net/ Typelite, looks promising and widely used.
3. Check this link http://littlebigtomatoes.com/2016/06/how-to-generate-typescript-classes-from-c-number-like-a-pro/ and explanation in it to generate typescript looks very easy (my personal recommendation after typeLite )
4. Web Essentials allow to compile C# files to TypeScript .d.ts files on save. Then you could reference the definitions from your .ts files.

If you are using Visual Studio 2015 or above (as TypeScriptSyntaxPaste needs the Rosalyn compiler), you can use TypescriptSyntaxPaste , you just need to install it from the Visual Studio Tools | Extensions menu, once you install it whenever you copy some C# code and paste it into a TypeScript file (either .ts or .tsx), TypeScriptSyntaxPaste will step in and will convert C# code to TypeScript. 

The above answer already mentions about it, you can consider below links for reference

http://littlebigtomatoes.com/2016/06/how-to-generate-typescript-classes-from-c-number-like-a-pro/

https://visualstudiomagazine.com/articles/2016/05/16/typescript-class-with-csharp.aspx

If anyone looking for a Visual Studio Code Extension for C# to Typescript converter, take a look at this one

https://marketplace.visualstudio.com/items?itemName=adrianwilczynski.csharp-to-typescript

Typescript to C# for VS code

https://marketplace.visualstudio.com/items?itemName=Box-Of-Hats.ts-to-csharp

For Visual Studio 2017 or above (C# to typescript)

https://marketplace.visualstudio.com/items?itemName=NhaBuiDuc.TypescriptSyntaxPaste