"application/json" constant in .NET framework

In order to add an up-to-date answer: since dotnet core 2.1 MediaTypeNames.Application.Json has been defined.

See https://github.com/dotnet/corefx/pull/26701 for the changeset.

See Newer Answer. This answer is now inaccurate.

While there are some MIME constants defined in MediaTypeNames (see here), there no constant for "application/json".

Putting additional content types in a shared const is probably best practice, better than defining them in string literals a million times throughout your code at least.

Plus it gives you the flexibility of using new/custom MIME types, which a specific .NET version might not have.