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Runtime libraries overview

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The .NET runtime has an expansive standard set of class libraries, known as runtime libraries, framework libraries, or the base class library (BCL). In addition, there are extensions to the runtime libraries, which are provided in NuGet packages.

These libraries provide implementations for many general and app-specific types, algorithms, and utility functionality.

Runtime libraries

The runtime libraries provide the foundational types and utility functionality and are the base of all other .NET class libraries. An example is the System.String class, which provides APIs for working with strings. Another example is the serialization libraries.

Extensions to the runtime libraries

Some libraries are provided in NuGet packages rather than as part of the runtime's shared framework. These libraries are often made available to apps that target downlevel .NET versions, such as .NET Framework, as well.

The following table shows some examples of package-provided libraries.

NuGet package Conceptual content
Microsoft.Extensions.Configuration Configuration
Microsoft.Extensions.DependencyInjection Dependency injection
Microsoft.Extensions.FileSystemGlobbing File globbing
Microsoft.Extensions.Hosting Generic Host
Microsoft.Extensions.Http HTTP
Microsoft.Extensions.Localization Localization
Microsoft.Extensions.Logging Logging

See also