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# ASP.NET 5 CompilerOptions - languageversion in project.json
- URL: https://blog.jsinh.in/asp-net-5-compileroptions-languageversion-in-project-json/
- Published: 2015-02-26T18:57:52.000Z
- Updated: 2026-07-07T15:07:26.000Z
- Author: Jsinh
- Tags: #Import 2026-10-04 19:16

**Note: \[Deprecated Content\]** This was written while ASP.NET and .NET Core was in beta (around beta5 or beta6). Since then a lot of stuffs have changed and moved around. Stuffs described below may or may not be true for current stable releases of ASP.NET Core. I recommend not to follow along and get confused. Use official configuration documentation that explains it correctly - [docs.asp.net](https://docs.asp.net/en/latest/index.html?ref=blog.jsinh.in)

ASP.NET 5 removed the `web.config` XML based configuration files and bring JSON based `project.json` and other similar files to maintain configuration related to your application.

`project.json` is the main file that contains meta-information / configuration for running your ASP.NET 5 application.

This JSON file consist of a node named `compilationOptions` which defines a child called `languageVersion`.

Currently ASP.NET 5 only supports C# language. `languageVersion` can be one of the following options:

![Choose C# language version](https://blob.jsinh.in/media/2015/02/27/SS01-ProjectJson-LanguageVersion-OptionValues.png)

It provides way to choose which version of C# you wish to use for your application to compile against.

I selected `csharp2` from the option intellisense list, added an `AutoProperty` and `Task` to my code. Visual studio immediately starts giving red swiglies similar to following:

![C# 2 selected and Task or AutoProperty does not work](https://blob.jsinh.in/media/2015/02/27/SS02-ProjectJson-LanguageVersion-CompilationWarning-Windows.png)

This change will also give error on Linux or MacOS X system when compiled:

![C# 2 selected and Task or AutoProperty does not work on linux](https://blob.jsinh.in/media/2015/02/27/SS03-ProjectJson-LanguageVersion-CompilationWarning-Linux.png)

I also see almost similar language version option in older version of ASP.NET and other project types in Visual Studio 2013\. I am not yet sure if it was already there before ASP.NET 5 but atleast now I know it and you know it too !!

![Language Version option in VS2013 - ASP.NET 4](https://blob.jsinh.in/media/2015/02/27/SS04-ASP.NET-4-VS2013-LanguageVersion.png)

**Note:** At the time of writing, ASP.NET 5 and .NET 4.6 are in BETA 3 and above information may change in future or final version.

Happy coding