CSharpist

What Is NuGet in .NET and C#?

When building applications with .NET and C#, you will often need functionality that someone else has already implemented. Instead of writing everything from scratch, you can use libraries created and maintained by other developers.

This is where NuGet comes in.

NuGet is the package manager for the .NET ecosystem. It makes it easy to find, install, update, and manage libraries and tools that your .NET applications depend on.

What Is a NuGet Package?

A NuGet package is a reusable piece of software that can be added to a .NET project.

Packages can contain:

  • C# or other .NET assemblies (.dll files)
  • Source code
  • Dependencies on other packages
  • Configuration files
  • Build tools
  • Documentation
  • Other files required by the library

For example, suppose you are building a C# application that needs to communicate with a REST API. You could write your own HTTP functionality, but you might instead use an existing library available as a NuGet package.

Some popular NuGet packages include libraries for:

  • JSON serialization
  • Database access
  • Logging
  • Dependency injection
  • Authentication
  • Testing
  • HTTP communication
  • Cloud services
  • Image processing

Why Do We Need NuGet?

Imagine that you want to use a library called ExampleLibrary in your C# application.

Without a package manager, you might have to:

  1. Find the library online.
  2. Download the correct version.
  3. Copy the DLL into your project.
  4. Find all of its dependencies.
  5. Download those dependencies manually.
  6. Configure your project to reference them.
  7. Repeat the process whenever the library is updated.

This quickly becomes difficult to maintain.

NuGet automates most of this process.

You can simply tell your .NET project that it depends on a particular package, and NuGet can download the package and its dependencies for you.

For example:

dotnet add package Newtonsoft.Json

NuGet downloads the package and adds it as a dependency of your project.

You can then use it from your C# code:

using Newtonsoft.Json;

var json = JsonConvert.SerializeObject(myObject);

The NuGet Gallery

NuGet packages are commonly distributed through the NuGet Gallery, the central public repository for .NET packages.

Developers can search for packages by name or functionality and see information such as:

  • Package versions
  • Dependencies
  • Download statistics
  • Documentation
  • Supported frameworks
  • License information
  • Links to the source code

For example, if you need a library for working with JSON, you can search NuGet for JSON-related packages.

However, it is important to remember that anyone can publish packages to public package repositories. Before adding a package to an important application, you should evaluate its publisher, source code, maintenance activity, dependencies, licensing, and security.

Adding a NuGet Package to a Project

There are several ways to install a NuGet package.

Using the .NET CLI

The .NET CLI provides the dotnet add package command:

dotnet add package Newtonsoft.Json

In newer .NET SDK versions, you may also encounter the equivalent project-management syntax:

dotnet package add Newtonsoft.Json

The exact command available depends on the .NET SDK version you are using.

Using Visual Studio

If you are using Visual Studio, you can manage packages through the NuGet Package Manager.

Typically, you can:

  1. Right-click your project.
  2. Select Manage NuGet Packages.
  3. Search for a package.
  4. Select the desired version.
  5. Install it.

Visual Studio then modifies the project so that the package becomes a dependency.

Editing the Project File

NuGet dependencies are commonly represented directly in a .csproj file.

For example:

<ItemGroup>
  <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
</ItemGroup>

This tells .NET that the project depends on Newtonsoft.Json version 13.0.3.

When you build or restore the project, NuGet obtains the required package.

What Is PackageReference?

Modern .NET projects generally use PackageReference to describe NuGet dependencies.

For example:

<PackageReference Include="Serilog" Version="4.0.1" />

The important parts are:

  • Include — the package ID.
  • Version — the package version.

These references are stored in the project file, making the project’s dependencies explicit and easy to reproduce on another machine.

What Is dotnet restore?

When a project contains NuGet dependencies, those packages need to be downloaded before the application can be built.

The command:

dotnet restore

restores the project’s dependencies.

For example, if your project contains:

<ItemGroup>
  <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
</ItemGroup>

dotnet restore finds the specified package and downloads it, along with the dependencies required by that package.

In many situations, you don’t need to run dotnet restore manually because commands such as dotnet build automatically perform a restore when necessary.

Where Are NuGet Packages Stored?

NuGet maintains a local package cache on your computer.

This is useful because multiple projects can use the same package without necessarily downloading the package again for every project.

The exact location depends on the operating system and configuration, but the default global packages folder is commonly located under the user’s profile.

You generally don’t need to interact with this folder directly.

Package Dependencies

One of NuGet’s most useful features is dependency management.

Suppose your application depends on:

MyApplication
    └── Package A
          └── Package B

Your application directly references Package A, while Package A requires Package B.

NuGet can discover and restore Package B automatically.

This is called a transitive dependency.

You therefore don’t necessarily have to add every dependency manually.

Package Versions

NuGet packages are versioned so that applications can specify which version they expect.

For example:

<PackageReference Include="SomeLibrary" Version="2.5.0" />

Versioning is important because a new version of a library can potentially introduce:

  • New features
  • Bug fixes
  • Performance improvements
  • Security fixes
  • Breaking changes

For production applications, dependency upgrades should therefore be deliberate rather than blindly upgrading everything to the newest version.

packages.lock.json

For applications where reproducible dependency resolution is important, NuGet can use a packages.lock.json file.

This file records the resolved versions of packages and their dependencies.

A lock file can help ensure that restoring a project produces a consistent dependency graph across environments.

This can be particularly useful in CI/CD pipelines and applications where deterministic builds are important.

NuGet and Source Control

A typical .NET project might look something like this:

MyApplication/
│
├── MyApplication.csproj
├── Program.cs
├── appsettings.json
└── ...

The .csproj file contains the project’s package references:

<ItemGroup>
  <PackageReference Include="Serilog" Version="4.0.1" />
</ItemGroup>

You normally do not commit the downloaded NuGet packages themselves into your source-control repository.

Instead, you commit the project configuration containing the package references.

When another developer clones the repository, they can run:

dotnet restore

and NuGet downloads the required dependencies.

This keeps the Git repository much smaller and makes dependency management reproducible.

NuGet Sources

NuGet can obtain packages from one or more package sources.

The most common source is the public NuGet Gallery, but organizations can also maintain private package repositories.

For example, a company might create an internal package:

Company.Logging
Company.Authentication
Company.Database

and publish those packages to a private NuGet feed.

This allows multiple applications within the organization to share common code without making those libraries publicly available.

NuGet in a CI/CD Pipeline

NuGet is also important when applications are built automatically.

A typical CI/CD process might look like:

Developer pushes code
        ↓
CI server checks out repository
        ↓
dotnet restore
        ↓
dotnet build
        ↓
dotnet test
        ↓
dotnet publish
        ↓
Application deployed

Because the project’s NuGet dependencies are defined in the project file, the build server can restore the same dependencies without developers manually copying libraries onto the server.

NuGet vs. DLL References

You might wonder why you shouldn’t simply copy a .dll file into your project.

You can, but NuGet provides several advantages.

With a manually referenced DLL, you have to manage things such as:

  • Where the DLL came from
  • Which version you are using
  • Its dependencies
  • How other developers obtain it
  • How it gets updated
  • How it is restored on a build server

With NuGet, much of this information becomes part of the project’s dependency configuration.

Instead of thinking:

“My application needs this DLL.”

you can think:

“My application depends on version X of this package.”

That distinction becomes increasingly important as applications grow.

NuGet Is More Than Just a Library Downloader

It is tempting to think of NuGet as simply a website where you download C# libraries.

It is more accurately a package-management ecosystem.

It handles concepts such as:

  • Package discovery
  • Package versions
  • Dependency resolution
  • Package restoration
  • Package sources
  • Package caching
  • Dependency graphs
  • Package publishing
  • Integration with .NET tooling and build systems

This makes NuGet an important part of modern .NET development.

A Simple Example

Suppose you create a new console application:

dotnet new console -n MyApp
cd MyApp

You decide that your application needs a particular third-party library.

You add it:

dotnet add package SomeLibrary

The project file now contains a package reference similar to:

<ItemGroup>
  <PackageReference Include="SomeLibrary" Version="1.2.3" />
</ItemGroup>

When you build the application:

dotnet build

.NET restores the required NuGet packages, compiles your C# code, and produces the application.

The important point is that the project’s dependency is described declaratively in the project file rather than requiring you to manually distribute DLLs.

Best Practices When Using NuGet

NuGet makes adding dependencies easy, but that doesn’t mean every package should automatically be added to a project.

A few good practices are:

1. Check the Package

Before installing a package, investigate who maintains it, whether it is actively maintained, its license, and its security history.

2. Avoid Unnecessary Dependencies

Every package adds another dependency to your application.

If a small feature can easily be implemented using functionality already available in .NET, adding a package may not be worthwhile.

3. Keep Dependencies Updated

Old dependencies can contain bugs or security vulnerabilities.

Regularly review and update important packages.

4. Be Careful With Major Version Updates

A major version change can introduce breaking changes.

Read the release notes before upgrading.

5. Use Private Feeds When Appropriate

Organizations should consider private NuGet feeds for internal libraries and proprietary packages.

6. Consider Reproducible Builds

For applications where build consistency matters, consider appropriate NuGet package-version and lock-file strategies.

Conclusion

NuGet is the package manager for the .NET ecosystem.

In a C# application, it provides a standardized way to add and manage external libraries and tools. Instead of manually downloading DLLs and managing their dependencies, you can declare your application’s dependencies in the project and let NuGet handle package restoration and dependency resolution.

A simple command such as:

dotnet add package SomeLibrary

can therefore represent much more than downloading a file. It establishes a managed dependency between your application and a versioned package in the .NET ecosystem.

If you work with modern .NET applications, understanding NuGet is essential because package management is a fundamental part of how .NET projects are built, tested, deployed, and maintained.