.SLN is dead. Long live .SLNX!

Everyone who has ever opened Visual Studio has encountered a .sln solution file that contains information about structure and build configuration, platform settings, and other parameters. Why create a new .slnx format after all these years? What are the differences between them? Let's break it down in this article.

The .sln format was created to streamline project management. The solution file enabled the grouping of related projects, which greatly simplified the processes of building and testing applications.

With each Visual Studio update, the .sln format evolved to support new languages such as C# and Visual Basic, as well as new technologies, and got improved integration with version control systems.

A retrospective look at the old .SLN

Although the .sln format has several advantages, it also has many disadvantages:

• Too large files. The .sln file is often quite large from the start, and adding projects quickly fills it with redundant identifiers and metadata.
• Useless duplicates. Many similar project names and solution parts is rudimentary and unhelpful.
• Difficult manual editing. Since the format is tool-oriented, manual editing the solution file often results in errors.
• Non-standard file format. The .sln format is proprietary, which limits its compatibility and integration options.

Now, let's take a look at an example of a solution file in the .sln format:

Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio Version 17
VisualStudioVersion = 17.0.31612.314
MinimumVisualStudioVersion = 10.0.40219.1
Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Radzen.Blazor", 
"Radzen.Blazor\Radzen.Blazor.csproj", 
"{30919FA8-6A6A-45A3-9B05-0B65ABF8F70F}"
EndProject
Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "RadzenBlazorDemos", 
"RadzenBlazorDemos\RadzenBlazorDemos.csproj", 
"{DF9EC444-791A-415A-A3EB-C4B008E5FCB5}"
EndProject
Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Radzen.Blazor.Tests", 
"Radzen.Blazor.Tests\Radzen.Blazor.Tests.csproj", 
"{BC20637F-A979-425A-9C3F-D72633FE555C}"
EndProject
Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "RadzenBlazorDemos.Host", 
"RadzenBlazorDemos.Host\RadzenBlazorDemos.Host.csproj", 
"{18702B3F-791E-45F3-BCFD-1792A1300AAB}"
EndProject
Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "RadzenBlazorDemos.Server", 
"RadzenBlazorDemos.Server\RadzenBlazorDemos.Server.csproj", 
"{EC869401-304A-45BC-93CA-C1CDFAAA7F7B}"
EndProject
Global
GlobalSection(SolutionConfigurationPlatforms) = preSolution
Debug|Any CPU = Debug|Any CPU
Release|Any CPU = Release|Any CPU
EndGlobalSection
GlobalSection(ProjectConfigurationPlatforms) = postSolution
{30919FA8-6A6A-45A3-9B05-0B65ABF8F70F}.Debug|Any 
CPU.ActiveCfg = Debug|Any CPU
{30919FA8-6A6A-45A3-9B05-0B65ABF8F70F}.Debug|Any 
CPU.Build.0 = Debug|Any CPU
{30919FA8-6A6A-45A3-9B05-0B65ABF8F70F}.Release|Any 
CPU.ActiveCfg = Release|Any CPU
{30919FA8-6A6A-45A3-9B05-0B65ABF8F70F}.Release|Any 
CPU.Build.0 = Release|Any CPU
{DF9EC444-791A-415A-A3EB-C4B008E5FCB5}.Debug|Any 
CPU.ActiveCfg = Debug|Any CPU
{DF9EC444-791A-415A-A3EB-C4B008E5FCB5}.Debug|Any 
CPU.Build.0 = Debug|Any CPU
{DF9EC444-791A-415A-A3EB-C4B008E5FCB5}.Release|Any 
CPU.ActiveCfg = Release|Any CPU
{DF9EC444-791A-415A-A3EB-C4B008E5FCB5}.Release|Any 
CPU.Build.0 = Release|Any CPU
{BC20637F-A979-425A-9C3F-D72633FE555C}.Debug|Any 
CPU.ActiveCfg = Debug|Any CPU
{BC20637F-A979-425A-9C3F-D72633FE555C}.Debug|Any 
CPU.Build.0 = Debug|Any CPU
{BC20637F-A979-425A-9C3F-D72633FE555C}.Release|Any 
CPU.ActiveCfg = Release|Any CPU
{BC20637F-A979-425A-9C3F-D72633FE555C}.Release|Any 
CPU.Build.0 = Release|Any CPU
{18702B3F-791E-45F3-BCFD-1792A1300AAB}.Debug|Any 
CPU.ActiveCfg = Debug|Any CPU
{18702B3F-791E-45F3-BCFD-1792A1300AAB}.Debug|Any 
CPU.Build.0 = Debug|Any CPU
{18702B3F-791E-45F3-BCFD-1792A1300AAB}.Release|Any 
CPU.ActiveCfg = Release|Any CPU
{18702B3F-791E-45F3-BCFD-1792A1300AAB}.Release|Any 
CPU.Build.0 = Release|Any CPU
{EC869401-304A-45BC-93CA-C1CDFAAA7F7B}.Debug|Any 
CPU.ActiveCfg = Debug|Any CPU
{EC869401-304A-45BC-93CA-C1CDFAAA7F7B}.Debug|Any 
CPU.Build.0 = Debug|Any CPU
{EC869401-304A-45BC-93CA-C1CDFAAA7F7B}.Release|Any 
CPU.ActiveCfg = Release|Any CPU
{EC869401-304A-45BC-93CA-C1CDFAAA7F7B}.Release|Any 
CPU.Build.0 = Release|Any CPU
EndGlobalSection
GlobalSection(SolutionProperties) = preSolution
HideSolutionNode = FALSE
EndGlobalSection
GlobalSection(ExtensibilityGlobals) = postSolution
SolutionGuid = {BD0EF65D-06F5-4DBD-BF9F-82CA04E26D8C}
EndGlobalSection
EndGlobal

GUIDs immediately catch the eye. No one would like to read such a file or deal with it. You can also easily see that the file is quite cumbersome, even though I tried to choose the shortest example of the .sln format.

Changes in the new .SLNX

On March 13, 2025, Microsoft published an article discussing the new .slnx solution format. However, there's neither an official release date nor documentation has been provided yet.

The .slnx format has been introduced as a new version of the .sln format. The most significant change is the adoption of the XML format, spaces, and comments. The .slnx format was designed to be concise and easy to read while preserving all the benefits of the original format.

Pros of the .slnx format over .sln:

• Improved readability for developers. It enables more efficient review and editing of solution files.
• The XML format support. Adopting the common XML format makes the new solution more flexible.
• Fewer merge conflicts. The streamlined file structure lowers the chance of merge conflicts in version control systems.

Here's an example of a solution file in the .slnx format:

<Solution>
  <Project Path="Radzen.Blazor.Tests/Radzen.Blazor.Tests.csproj" />
  <Project Path="Radzen.Blazor/Radzen.Blazor.csproj" />
  <Project Path="RadzenBlazorDemos.Host/RadzenBlazorDemos.Host.csproj" />
  <Project Path="RadzenBlazorDemos.Server/RadzenBlazorDemos.Server.csproj" />
  <Project Path="RadzenBlazorDemos/RadzenBlazorDemos.csproj" />
</Solution>

That's it!? Yep, that's the full solution file.

To try a new format, save your solution in that format (sounds logical). In Visual Studio, open File > Save Solution As and select XML Solution File (*.slnx) as the extension.

You can also save the solution in the new format via Rider, by clicking Save as > Save as XML Solution (.slnx).

If you don't want to or can't migrate to the new format via an IDE for some reason, you can use the following command:

dotnet SLN <YourSolutionFile.SLN> migrate

New format limitations

However, don't rush to migrate all your projects to the new solution format. Many developers are delaying it because the new .slnx format is still in the early development stages.

Since .slnx is a new format, many third-party tools, plugins, and CI/CD systems still work only with .sln files. Plus, some features are unsupported at this stage. Finally, there's no detailed documentation, and issues may arise if you use different file formats.

However, MSBuild now fully supports .slnx, providing seamless integration with .NET build systems and C++. The .NET CLI has also been updated to handle the new format. The C# Dev Kit offers extensive support for .slnx files, simplifying solution file management within the VS Code environment.

The new format is still considered a preview feature and hasn't been officially released yet. However, the dev community has responded positively to the new feature. Some large projects have already migrated to .slnx—for example, the Files project for file management has made the switch.

Conclusion

The new .slnx format is a potential successor to the old proprietary .sln. However, no widespread migration is expected anytime soon since the format has yet to be officially released.

Still, some major tools like MSBuild and the .NET CLI already fully support .slnx. Starting with PVS-Studio 7.37, the analyzer also supports analysis based on the new solution format. Don't worry though, the process of running the analysis hasn't changed for users—just click the correct button in the IDE as usual.

I think that by the official release, more tools will support .slnx, meaning the number of migrations will likely increase in the future.

Please share your thoughts on the new feature in comments. Also, if you already experienced the project migration to the new solution format, we'd be happy to hear from you!

As usual, you can request a trial of the new PVS-Studio version on our website :)