The Csharp SDK from Modelcontextprotocol is the official C# SDK for the Model Context Protocol (MCP). It enables .NET applications, services, and libraries to implement and interact with MCP clients and servers. This SDK connects to MCP servers and clients, standardizing how applications provide context to Large Language Models (LLMs) for secure integration with data sources and tools. Distributed as NuGet packages, it supports various .NET environments. The Csharp SDK is categorized as an MCP server tool, yet it supports both client and server implementations, offering versatility for developers building AI-powered solutions.

What does Csharp SDK connect to?

The Csharp SDK connects to Model Context Protocol (MCP) servers and clients. The MCP is an open protocol designed to standardize how applications provide context to Large Language Models (LLMs). This standardization enables secure integration between LLMs and various data sources and tools. While categorized as an MCP server tool, the SDK supports both client and server implementations, allowing .NET applications to act as either an MCP client or a server within the protocol ecosystem.

Core features and tools

The SDK exposes callable tools, resources, and prompts for interaction with LLMs. Developers can create specific callable tools using McpServerTool.Create. It also supports McpServerPrompt and McpServerResource primitives for defining interactions. Tool invocation is handled through structured JSON inputs and outputs, ensuring clear communication. The SDK supports both local and remote transport protocols, including HTTP-based MCP servers via ModelContextProtocol.AspNetCore and stream-based transport using System.IO.Pipelines.

Who is it for?

The Csharp SDK is primarily for .NET developers building AI copilots, agent frameworks, or tool-augmented LLM applications. It is particularly useful for those requiring cross-language interoperability or needing to maintain shared tool services across different programming environments. AI clients built with any MCP-compatible SDK, including TypeScript, Python, Go, Rust, Java, Ruby, Swift, PHP, and Kotlin, are confirmed compatible. Skip this if your project does not involve integrating .NET applications with the Model Context Protocol.

How to get started

Access is granted through a standard OAuth authorization flow. Setup involves configuring Protected Resource Metadata (PRM) using the AddMcp extension method on AuthenticationBuilder, specifying ResourceMetadata including AuthorizationServers and ScopesSupported. The SDK supports the Identity Assertion Authorization Grant flow via IdentityAssertionGrantProvider. HTTP-based MCP servers are supported via ModelContextProtocol.AspNetCore.

Use cases

• Tool Calling/Invocation: LLMs request tools, the server executes them, and responses are integrated into the LLM's ongoing interaction.
• Long-running Operations: Supports asynchronous tool invocations with status polling and input requests, integrating with existing workflow systems like CI/CD pipelines.
• Interactive UI Applications: Enables building dynamic user interfaces that render within MCP hosts.

The Csharp SDK provides .NET developers with a structured way to build applications interacting with the Model Context Protocol. It supports both client and server implementations, offering tools, resources, and prompts for LLM integration. The SDK's compatibility with various language SDKs and its authentication model make it suitable for complex AI projects. Its support for different transport protocols adds to its adaptability. Try creating a callable tool using McpServerTool.Create to handle LLM requests.