Microsoft has partnered with Anthropic to develop a C# Software Development Kit (SDK) for the Model Context Protocol (MCP), an open protocol designed to connect large language models with external tools and data sources. The open-source SDK is now available under the modelcontextprotocol GitHub organization.
Based on an existing community project called mcpdotnet, the C# SDK builds upon Peder Holdgaard Pederson’s groundwork. Microsoft acknowledged his contributions, calling him a key partner in shaping the release.
The MCP protocol allows applications to communicate with tool- and resource-hosting servers in a standardized way, defining messages and behaviors for tool execution and resource access. Several Microsoft products have already adopted MCP internally.
Robert Recalde, principal engineer at Cigna Healthcare, emphasized the significance of the SDK: “This partnership significantly expands our ability to integrate AI capabilities into .NET applications.”
The protocol supports standard messages like ListToolsRequest and ReadResourceRequest, enabling agentic applications to reason across a wider context. Microsoft plans to support authentication protocols like OAuth and OpenID Connect in the near future.
Developers can access the SDK now via NuGet, along with documentation, samples, and source code in the official GitHub repository.
Source: https://www.infoq.com/news/2025/04/microsoft-csharp-sdk-mcp