Setting the file. One moment.
Subchapter 143.4
references/packages.mdMarkdown5 KBView on GitHub
All packages live under the ModelContextProtocol NuGet profile (opens in a new tab). The official C# SDK repo is modelcontextprotocol/csharp-sdk (opens in a new tab), maintained jointly by the MCP project and Microsoft.
| Package | When to use it | Brings in |
|---|---|---|
ModelContextProtocol | Default for STDIO servers and most projects | Core + Microsoft.Extensions.Hosting integration, attribute discovery (AddMcpServer, WithToolsFromAssembly, etc.) |
ModelContextProtocol.AspNetCore | HTTP (Streamable) servers hosted in ASP.NET Core | The above + WithHttpTransport and MapMcp |
ModelContextProtocol.Core | Pure clients, custom hosts, low-level scenarios where you don’t want the Microsoft.Extensions.* dependencies | Just the protocol + transports + low-level McpServer.Create / McpClient.CreateAsync |
ModelContextProtocol.Extensions.Tasks (2.x) | Long-running task support (the MCP Tasks extension) | Production replacement for the experimental 1.4.x Tasks APIs; register via WithTasks(...) |
ModelContextProtocol.Extensions.Apps (2.x) | MCP Apps — interactive UI rendered in the host | Typed [McpAppUi] attribute + .WithMcpApps() registration replacing the hand-rolled _meta wiring of 1.x; you still serve the UI as a ui:// resource, and the APIs are experimental (MCPEXP003) — see mcp-apps.md |
Rule of thumb:
ModelContextProtocol + Microsoft.Extensions.Hosting.ModelContextProtocol.AspNetCore only (it transitively pulls in everything you need).ModelContextProtocol.Core (or ModelContextProtocol if you also want hosting/DI for the client).As of mid-2026, the stable line is 2.x (2.2.0 is current at time of writing), aligned with the MCP 2026-07-28 spec. The 0.x line was preview and has breaking differences — if you find docs or blog posts referencing 0.4/0.6, treat them as out of date. The 1.x line still compiles and interoperates, but predates the v2 changes (stateless-by-default HTTP, discovery-first negotiation, roots/sampling/logging deprecations, the Tasks/Apps extension packages) — prefer 2.x for new projects.
Upgrading 1.x → 2.0 (highlights, not exhaustive): stable v1.x APIs keep working; the deprecated capabilities (roots, sampling, logging) are now [Obsolete] with MCP9005 warnings, experimental APIs moved (the 1.4.x Tasks surface → ModelContextProtocol.Extensions.Tasks), and several behaviors flipped (HttpServerTransportOptions.Stateless now defaults to true; non-object tool results emit raw structuredContent values; Tool.inputSchema is required on deserialization). OAuth also changed at runtime — AuthorizationRedirectDelegate → ClientOAuthOptions.AuthorizationCallbackHandler, RFC 9207 issuer validation, mandatory PKCE S256 in metadata, application_type in dynamic registration — and SSE transport failures now propagate the underlying HttpRequestException/TimeoutException. Before upgrading, read the full v2.0.0 release notes (opens in a new tab).
To check the latest:
dotnet search ModelContextProtocol --prereleaseThe SDK targets .NET 8.0 and netstandard2.0. That means it runs on:
For HTTP servers you specifically need a TFM that supports ASP.NET Core (so .NET 8/9/10).
dotnet new console -n MyMcpServer -f net10.0
cd MyMcpServer
dotnet add package ModelContextProtocol --version 2.2.0
dotnet add package Microsoft.Extensions.Hosting --version 10.0.11dotnet new web -n MyMcpServer -f net10.0
cd MyMcpServer
dotnet add package ModelContextProtocol.AspNetCore --version 2.2.0(dotnet new web gives you a minimal ASP.NET Core project — exactly what MapMcp needs.)
dotnet new console -n MyMcpClient -f net10.0
cd MyMcpClient
dotnet add package ModelContextProtocol.Core --version 2.2.0| Package | Why |
|---|---|
Microsoft.Extensions.AI | Provides IChatClient, ChatMessage, ChatRole, ChatOptions — the abstractions used by AsSamplingChatClient() and by prompt return types. |
Microsoft.Extensions.AI.Abstractions | Pulled in transitively but worth knowing about for types like DataContent, TextContent. |
OpenTelemetry.Extensions.Hosting | The SDK emits OTel traces and metrics for tool calls — wire them up if the user has an observability story. |
Newer Microsoft examples sometimes show launching servers via dnx PackageName --version 1.2.3. That’s a valid distribution model: publish your server as a NuGet package and let users run it without cloning. It’s orthogonal to how the server itself is built — keep your code identical and just change the launch command.