Building libraries with .NET Core

Targeting .NET Standard

{
   "description": "My awesome library",
   "dependencies": {
      "NETStandard.Library": "1.6.0"
   },
   "frameworks": {
      "netstandard1.3": { }
   }
}

A library that targets netstandard1.3 can be used on any framework that supports .NET Standard 1.3 or later. Choosing a lower .NET Standard version for a library means that more projects can use it, but less APIs are available.

Targeting both .NET Standard and .NET Framework 4.x

{
   "description": "My awesome library",
   "dependencies": { },
   "frameworks": {
      "net40": { },
      "netstandard1.3": {
         "dependencies": {
            "NETStandard.Library": "1.6.0"
         }
      }
   }
}

By targeting both net40 and netstandard1.3, the library will work in both .NET 4.0+ projects and .NET Standard projects. It’s important to move the NETStandard.Library dependency into the netstandard1.3 section so it’s only referenced when building for that framework.

Producing a NuGet package for a library

Any project that targets netstandard1.X can be packed into a NuGet package by running:

dotnet pack

The resulting package can be uploaded to NuGet, MyGet, or hosted in a local package source.

Platform-specific dependencies

You can specify different dependencies for each platforms:

"net45": {
    "frameworkAssemblies": {
        "System.Linq": "4.1.0"
    }
},
"netstandard1.3": {
    "dependencies": {
        "NETStandard.Library": "1.6.0",
        "System.Linq": "4.1.0-rc2"
    }
},
"netstandard1.4": {
    "dependencies": {
        "NETStandard.Library": "1.6.0",
        "System.Linq": "4.1.0"
    }
}

When this project is compiled and packed, each framework target will use a different set of dependencies:

• net45 (projects targeting .NET 4.5+) will use the System.Linq assembly from the GAC.
• netstandard1.3 (.NET Core projects targeting .NET Standard 1.3) will use the NETStandard.Library version 1.6.0 NuGet package, and the System.Linq prerelease version 4.1.0-rc2 NuGet package.
• netstandard1.4 will use the same version of NETStandard.Library, but the release 4.1.0 version of System.Linq.

Adding a project reference to a library

If you have multiple libraries in the same solution, you can add local (project) references between them:

{
   "dependencies": {
      "NETStandard.Library": "1.6.0",
      "MyOtherLibrary": {
        "target": "project"
      }
   },
   "frameworks": {
      "netstandard1.3": { }
   }
}

The target: project property value tells NuGet to look in the current solution for MyOtherLibrary, instead of in your package sources.