This directory contains the C# Protocol Buffers runtime library.


The easiest way how to use C# protobufs is via the Google.Protobuf NuGet package. Just add the NuGet package to your VS project.

You will also want to install the Google.Protobuf.Tools NuGet package, which contains precompiled version of protoc.exe and a copy of well known .proto files under the package's tools directory.

To generate C# files from your .proto files, invoke protoc with the --csharp_out option.

Supported platforms

The runtime library is built as a class library, supporting targets of:

  • .NET 4.5+ (net45)
  • .NET Standard 1.1 and 2.0 (netstandard1.1 and netstandard2.0)
  • .NET 5+ (net50)

You should be able to use Protocol Buffers in Visual Studio 2012 and all later versions. This includes all code generated by protoc, which only uses features from C# 3 and earlier. When compiling generated code with old compilers (before C# 7.2) you need to define the GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE symbol in your project so that the generated classes don't implement IBufferMessage, which uses ref struct types.


Open the src/Google.Protobuf.sln solution in Visual Studio 2022 or later.

Although users of this project are only expected to have Visual Studio 2012 or later, developers of the library are required to have Visual Studio 2022 or later, as the library uses C# 10 features in its implementation and runs tests under .NET 6. These features have no impact when using the compiled code - they're only relevant when building the Google.Protobuf assembly.


The unit tests use NUnit 3. Tests can be run using the Visual Studio Test Explorer or dotnet test.

.NET 3.5

We don't support .NET 3.5. It used to be feasible to build this library targeting .NET 3.5, but a number of changes requiring newer runtime/framework features have been added over time. While it would no doubt be possible to rework the current implementation to allow most of the functionality to be built in .NET 3.5, this would create an undue maintenance burden.

History of C# protobufs

This subtree was originally imported from and represents the latest development version of C# protobufs, that will now be developed and maintained by Google. All the development will be done in open, under this repository (

The previous project differs from this project in a number of ways:

  • The old code only supported proto2; the new code initially only supported proto3 (so no unknown fields, no required/optional distinction, no extensions); since then proto2 support has been added
  • The old code was based on immutable message types and builders for them
  • The old code did not support maps or oneof
  • The old code had its own JSON representation, whereas the new code uses the standard protobuf JSON representation
  • The old code had no notion of the “well-known types” which have special support in the new code
  • The old project supported some older platforms (such as older versions of Silverlight) which are not currently supported in the new project