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Recommended reading to better understand this document: .NET Standard | Project-Guidelines | Package-Projects

Add APIs

Determine what library

  • Propose a library for exposing it as part of the API review process.
  • Keep in mind the API might be exposed in a reference assembly that doesn't match the identity of the implementation. There are many reasons for this but the primary reason is to abstract the runtime assembly identities across different platforms while sharing a common API surface and allowing us to refactor the implementation without compat concerns in future releases.

Determine target framework

net11.0 is the target framework version currently under development and the new apis should be added to net11.0. More Information on TargetFrameworks

Making the changes in repo

Implement your API modification

  • Implement your API modification in the appropriate library project.

Update the reference source

Update tests

  • Add new TargetFramework to the TargetFrameworks.
  • Add new test code following conventions for new files to that are specific to the new target framework.
  • To run just the new test targetFramework run dotnet build <Library>.csproj -f <TargetFramework> /t:Test. TargetFramework should be chosen only from supported TargetFrameworks.

Documentation

New public APIs must be documented with triple-slash comments on top of them. Visual Studio automatically generates the structure for you when you type ///.

API writing guidelines has information about language and proper style for writing API documentation. If your new API or the APIs it calls throw any exceptions, those need to be manually documented by adding the <exception></exception> elements.

After your change is merged, we will eventually port them to the dotnet-api-docs repo. The tools used for this port live in api-docs-sync repo. Once the dotnet-api-docs change is merged, your comments will start showing up in the official API documentation at https://learn.microsoft.com, and later they'll appear in IntelliSense in Visual Studio and Visual Studio Code.

The rest of the documentation workflow depends on whether the assembly has the UseCompilerGeneratedDocXmlFile property set in its project file:

For libraries without this property (or with it set to true, which is the default):

  • Source comments in this repo are the source of truth for documentation.
  • Triple-slash comments in source code are synced to dotnet-api-docs periodically (every preview).
  • More recently introduced libraries typically follow this workflow.

Documentation placement in platform-specific libraries

When a library targets platform-specific frameworks (e.g. net11.0-windows, net11.0-linux), only one platform's compiler-generated doc XML is selected as the source of truth and shipped to all customers in the IntelliSense package. This means that if XML doc comments for a public API appear only in a platform-specific partial file, they may be missing from the shipped docs on other platforms.

To ensure consistent documentation across all platforms, follow these rules:

  1. Place docs on the primary source file. Each public type should have a primary source file named TypeName.cs. All public API documentation (/// <summary>, /// <param>, etc.) must be placed in this file.
  2. Follow the naming convention for partial files. Platform-specific or feature-specific partials must follow the TypeName.Something.cs naming convention (e.g. Socket.Windows.cs, Socket.Unix.cs).
  3. Do not add public XML doc comments in non-primary partial files. If a public member is declared in a file like TypeName.Windows.cs, its documentation should be in TypeName.cs (using a partial method declaration or <inheritdoc/>), not in the platform-specific file.

These rules are enforced by the PlatformDocAnalyzer (eng/analyzers/PlatformDocAnalyzer), which is automatically applied to all library source projects. The analyzer only activates when building a platform-specific target framework with UseCompilerGeneratedDocXmlFile=true, and produces the following diagnostics:

Diagnostic Description
PLATDOC001 Public type has no source file named TypeName.cs.
PLATDOC002 Partial source file doesn't follow the TypeName.Something.cs naming convention.
PLATDOC003 Public member in a non-primary partial file has XML documentation that should be moved to TypeName.cs.
PLATDOC004 Documentation for a public API differs from the canonical (platform-agnostic) build.

PLATDOC001–003 are heuristic rules that guide source organization. PLATDOC004 is an authoritative check: when a project also targets a platform-agnostic TFM (e.g. net11.0 alongside net11.0-windows), the build passes the canonical TFM's compiler-generated doc XML to the analyzer, which compares each public API's documentation against it. Any mismatch indicates that docs were placed on platform-specific source and will be inconsistent across platforms.

If a file legitimately doesn't follow these conventions (e.g. an Async partial using the established TypeNameAsync.cs pattern), suppress the specific diagnostic with #pragma warning disable PLATDOCnnn and a brief comment explaining why.

For libraries with <UseCompilerGeneratedDocXmlFile>false</UseCompilerGeneratedDocXmlFile>:

  • The dotnet-api-docs repo is the source of truth for documentation.
  • Triple-slash comments in source code are synced to dotnet-api-docs only once for newly introduced APIs. After the initial sync, all subsequent documentation updates must be made directly in the dotnet-api-docs repo.
  • It's fine to make updates to the triple-slash comments later to aid local development, they just won't automatically flow into the official docs. Copilot can help with porting small changes in triple-slash comments to dotnet-api-docs. PortToDocs tool works better for ports of large changes.
  • Older libraries typically follow this workflow. Libraries in this mode can work towards a better workflow in the future by using api-docs-sync tools to port back docs to source, then removing the UseCompilerGeneratedDocXmlFile property.

FAQ

What to do if you are moving types down into a lower contract?

If you are moving types down you need to version both contracts at the same time and temporarily use project references across the projects. You also need to be sure to leave type-forwards in the places where you removed types in order to maintain back-compat.