For years, you’ve worked with Visual Studio’s solution file (*.SLN) format, and while it’s a core part of your project organization, we know the experience hasn’t always been smooth. Whether you’ve been modifying, maintaining, or trying to resolve merge conflicts, it’s often felt more like a hassle than it should be. We understand your frustrations, and we’re here to talk about why it’s time for a change and how a new solution file format can make your life easier.

The Challenges Copy link

Despite being a critical element of the Visual Studio ecosystem, the existing solution file format has its share of drawbacks:

• Manual Edits Are Tedious: Editing solution files manually is error-prone due to its tool-centric format. Small mistakes often lead to misconfigurations, disrupting your workflow.
• Merge Conflicts Are a Constant Issue: In team environments, merge conflicts in solution files can cause lost work, corrupted files, and delays, making it harder to focus on building software.
• Verbosity and Redundancy: Solution files start with over 200 characters, and as you add projects, they quickly become bloated with duplicate GUIDs and metadata, cluttering your work.
• No Real Benefit from Duplication: Redundant references to project names and solution items provide little value and only add confusion, taking up space without improving your workflow.
• Non-Standard File Format: The .SLN file format is specific to Visual Studio and not a widely recognized standard, which limits its compatibility with external tools and automation.

To help you visualize these challenges, here’s an example of a traditional Visual Studio solution file: Copy link

Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio Version 17
VisualStudioVersion = 17.9.34511.98
MinimumVisualStudioVersion = 10.0.40219.1
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "DotNetMonitorWebApp", "DotNetMonitorWebApp\DotNetMonitorWebApp.csproj", "{1385B389-B20C-4D19-8FE0-85629BC41343}"
EndProject
Global
GlobalSection(SolutionConfigurationPlatforms) = preSolution
Debug|Any CPU = Debug|Any CPU
Release|Any CPU = Release|Any CPU
EndGlobalSection
GlobalSection(ProjectConfigurationPlatforms) = postSolution
{1385B389-B20C-4D19-8FE0-85629BC41343}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
{1385B389-B20C-4D19-8FE0-85629BC41343}.Debug|Any CPU.Build.0 = Debug|Any CPU
{1385B389-B20C-4D19-8FE0-85629BC41343}.Release|Any CPU.ActiveCfg = Release|Any CPU
{1385B389-B20C-4D19-8FE0-85629BC41343}.Release|Any CPU.Build.0 = Release|Any CPU
EndGlobalSection
GlobalSection(SolutionProperties) = preSolution
HideSolutionNode = FALSE
EndGlobalSection
GlobalSection(ExtensibilityGlobals) = postSolution
SolutionGuid = {C12E911E-FAA3-4ACE-B6BF-C3605E866483}
EndGlobalSection
EndGlobal

Simplifying the Solution File Copy link

We’ve made several improvements with the new solution file format to enhance your experience. These changes include a more readable and editable structure, the use of a XML format, and the preservation of whitespace and comments for better organization. The new format is minimalistic, optimizing performance for faster load times, and reduces merge conflicts in version control. It also ensures compatibility with older Visual Studio versions and aligns with certain MSBuild conventions for smoother integration with other tools.

Here’s a detailed look at these enhancements:

• Human-Readable and Editable: The new solution file format is designed with clarity in mind, making it easy for developers to read and modify project configurations. This eliminates much of the confusion and errors that arose from manually editing complex files.
• Standardized XML Format: We’ve moved away from a proprietary format and adopted XML for the solution file structure. XML is widely understood, offering flexibility and standardization for greater ease of use.
• Whitespace and Comment Preservation: We now preserve whitespace and comments within solution files when saving them, ensuring your formatting stays intact and helping to maintain an organized file.
• Minimalistic Footprint: The new format adopts sensible defaults, keeping the solution file minimal and optimizing performance. This leads to efficient use of resources, even for large solutions.
• Reduced Merge Conflicts: By simplifying the file structure, we’ve reduced the likelihood of merge conflicts in version control systems. This means fewer headaches when collaborating with teammates and easier management of changes.
• Compatibility with Older Visual Studio Versions: We’ve ensured compatibility with Visual Studio Dev 17.14, allowing a smooth transition between the old and new file formats without disrupting your workflow.
• Alignment with MSBuild: The new format aligns with certain MSBuild conventions, which enhances its integration with other tools and platforms, ensuring smoother interoperability.

To give you a glimpse into the simplicity of the new .SLNX format, here’s an example: Copy link

<Solution>
<Project Path="DotNetMonitorWebApp\DotNetMonitorWebApp.csproj" />
</Solution>

To save a solution in the new file format, select the solution node in Solution Explorer, then go to File -> Save Solution As… and choose the “XML Solution File (*.SLNX)” format. The solution will then be saved as a .SLNX file.

To open a .SLNX file, use the File -> Open command and select the .SLNX file. Note that Visual Studio is not registered as the default handler for .SLNX files, so they won’t open in Visual Studio by default.

Frequently Asked Questions (FAQ) Copy link

If you have questions about or are curious to learn more about the format and our plans, have a read of the FAQ section below.

What is a solution file? Copy link

A Visual Studio solution file (.SLN extension) is essential for organizing and managing multiple projects within Visual Studio. It acts as a container that maintains references between projects, build configurations, and other settings, defining how the solution is structured, and which projects are involved.

What support is available for the .SLNX format across different tools and environments? Copy link

We are currently working on providing support for the. SLNX format across various tools and environments. Here’s what you can expect:

• MSBuild Support: MSBuild now fully supports the .SLNX format, enabling seamless integration with the .NET and C++ build systems. This support allows for efficient building, adding, and removing projects within .SLNX files using MSBuild commands.
• .NET CLI Support: The .NET CLI has been updated to handle .SLNX files, providing consistent experience for managing solutions directly from the command line.
• C# Dev Kit Support: The C# Dev Kit for VS Code now fully supports the .SLNX format, making it easier to work with solution files within the VS Code environment.

What about third-party tool support? Copy link

The .SLNX file format is designed for wide adoption, but we recommend waiting until it’s more finalized before fully adopting it.

If you’re using tools that rely on either the .SLN or .SLNX file formats, we have developed an open source serializer that supports both formats: vs-solutionpersistence.

Can I edit .SLNX files without unloading? Copy link

Like .SLN files, .SLNX files must be unloaded to be edited in Visual Studio. However, we don’t anticipate many cases where manual editing will be necessary. If you’d like to see support for editing without unloading, we encourage you to upvote the community request.

What about solution filters? Copy link

Solution filters (.SLNf files), which help improve load and run times, will continue to work with the new .SLNX format — but keep in mind that filter files are tied to a specific solution file. If you migrate your solution from .SLN to .SLNX, you’ll need to update the filter file to reference the new .SLNX file, otherwise it will still try to open the old .SLN file.

Will extensions continue to support. SLNX? Copy link

We designed the .SLNX file format to be transparent to extensions. Existing Visual Studio APIs that work with .SLN files should continue to work without requiring changes. However, if your extension directly edits solution files, it will need to support both .SLN and .SLNX formats. To learn more about working with solution files in extensions, we recommend checking out the vs-solutionpersistence library, which provides useful APIs for solution file manipulation

How do I migrate from the old .SLN format to .SLNX? Copy link

Migrating from the traditional .SLN format to the new .SLNX format is simple, and there are two ways to do it:

• Using the .NET CLI (for .NET projects)

For .NET developers, you can migrate your solution using the following command:

dotnet SLN <YourSolutionFile.SLN> migrate

Replace <YourSolutionFile.SLN> with the actual name of your solution file. This command will generate a .SLNX file from your existing .SLN file.

• Using Visual Studio (recommended for all languages)

Once the .SLNX feature is enabled, you can save your solution in the new format directly from Visual Studio — this method works for all supported project types, including C++, Python, JS/TS, and others.

To save in the new format:

1. 1. Right-click the solution node in Solution Explorer.
   2. Select File -> Save Solution As….
   3. In the file type dropdown, choose Xml Solution File (*.SLNX).
   4. Click Save.

Can I have both .SLN and .SLNX files in the same repo? What’s the best practice for teams where some clients still use .SLN and others want to move to .SLNX? Copy link

We strongly recommend not having both .SLN and .SLNX files in the same repository. This can cause issues such as:

• Commands like dotnet SLN will not automatically detect the correct solution file.
• Keeping both files manually in sync can be error-prone and lead to confusion across teams.

If you absolutely need to maintain both for compatibility reasons (e.g., during a phased migration), consider using a sync tool like this one: dotnet-SLN-sync, which helps automatically keep .SLN and .SLNX files aligned.

However, the recommended best practice is to coordinate the transition with all clients and move fully to .SLNX once the entire team or organization is ready.

Disclaimer: The dotnet-sln-sync tool is a community-developed project and is not maintained or supported by Microsoft. Please use it at your discretion.

Will file globbing be supported? Copy link

The current solution design lists all projects and their locations directly in the solution file. This approach allows Visual Studio to begin loading projects almost immediately.

Supporting globbing, would require scanning the file system and evaluating potentially complex patterns to identify matching projects. Especially for larger repositories, this additional step can significantly slow down the loading process which is why globbing is not currently supported.

For those unfamiliar, globbing refers to pattern matching used to dynamically resolve file paths, commonly seen in many build systems and tools. You can read more about this concept here.

Why did you choose XML for .SLNX? Copy link

We selected XML because it’s a widely used format, and it’s the same format used by project files. XML in project files supports powerful evaluation and execution capabilities, but we want to keep .SLNX simple for now. We’re focused on maintaining the basic functionality like .SLN while keeping things straightforward.

What are the minimum supported tooling versions for building with >SLNX format, and what scenarios are currently unsupported? Copy link

To build with the .SLNX format:

• If you’re building with .NET, ensure the project’s global.json is set to a minimum of .NET 9.0.200 SDK.
• If you’re building with MSBuild, make sure your build tools are using Visual Studio or Build Tools for Visual Studio version 17.13 or later.

Looking Ahead: Your Feedback Is Key Copy link

Your feedback shapes the future of Visual Studio, and we truly appreciate the time you take to share it. Whether it’s a bug report or a new feature idea, your insights help us build a better experience for you.

Got feedback? Let us know!

• Report a Problem – If something isn’t working as expected, tell us on Developer Community.
• Suggest a Feature – Have an idea to make Visual Studio even better? We’re listening!

To stay in the loop on the latest updates, tips, and discussions from the Visual Studio team connect with the us on the Visual Studio Hub .