\n2025-11-25 version of the MCP Specification<\/a>.
\nThis release delivers a rich set of new capabilities \u2014 from improved authorization flows and richer metadata,
\nto powerful new patterns for tool calling, elicitation, and long-running request handling.<\/p>\n
Here\u2019s a tour of what\u2019s new.<\/p>\n
Enhanced authorization server discovery<\/h2>\n
In the previous spec, servers were required to provide a link to their Protected Resource Metadata (PRM) Document Clients check these locations in order.<\/p>\n On the server side, the SDK\u2019s AddMcp extension method on AuthenticationBuilder<\/a> When configured this way, the SDK automatically hosts the PRM Document at the well-known location The 2025-11-25 spec adds icon metadata to Tools, Resources, and Prompts. This information is included The simplest way to add an icon for a tool is with the IconSource parameter on the McpServerToolAttribute<\/a>:<\/p>\n The McpServerResourceAttribute<\/a>, For more advanced scenarios \u2014 multiple icons, MIME types, size hints, and theme preferences \u2014 you can Here\u2019s how these icons could be displayed, as illustrated in the MCP Inspector:<\/p>\n This placement works well after the code example showing how to configure multiple icons, providing a visual demonstration of how those icons appear in practice.<\/p>\n The Implementation<\/a> class also has The incremental scope consent feature brings the Principle of Least Privilege<\/a> MCP uses OAuth 2.0 for authorization, where scopes<\/em> define the level of access a client has. The mechanism works through two flows:<\/p>\n Initial scopes<\/strong>: When a client makes an unauthenticated request, the server responds with Additional scopes<\/strong>: When a client\u2019s token lacks scopes for a particular operation, the server The MCP C# client SDK handles incremental scope consent automatically. When it receives a Setting up incremental scope consent on the server involves:<\/p>\n Adding authentication services<\/strong> configured with the MCP authentication scheme:<\/p>\n Enabling JWT bearer authentication<\/strong> with appropriate token validation:<\/p>\n The following token validation settings are strongly recommended:<\/p>\n
\nin the resource_metadata<\/code> parameter of the WWW-Authenticate<\/code> header.
\nThe 2025-11-25 spec broadens this, giving servers three ways to expose the PRM:<\/p>\n\n
resource_metadata<\/code> parameter of the WWW-Authenticate<\/code> header (as before)<\/li>\n
\n(e.g. https:\/\/example.com\/.well-known\/oauth-protected-resource\/public\/mcp<\/code>)<\/li>\nhttps:\/\/example.com\/.well-known\/oauth-protected-resource<\/code>)<\/li>\n<\/ol>\n
\nmakes it easy to configure the PRM Document:<\/p>\n.AddMcp(options =>\n{\n options.ResourceMetadata = new()\n {\n ResourceDocumentation = new Uri(\"https:\/\/docs.example.com\/api\/weather\"),\n AuthorizationServers = { new Uri(inMemoryOAuthServerUrl) },\n ScopesSupported = [\"mcp:tools\"],\n };\n});<\/code><\/pre>\n
\nand includes the link in the WWW-Authenticate<\/code> header. On the client side, the SDK handles the
\nfull discovery sequence automatically.<\/p>\nIcons for tools, resources, and prompts<\/h2>\n
\nin the response to tools\/list<\/code>, resources\/list<\/code>, and prompts\/list<\/code> requests.
\nImplementation metadata (describing a client or server) has also been extended with icons and a website URL.<\/p>\n[McpServerTool(Title = \"This is a title\", IconSource = \"https:\/\/example.com\/tool-icon.svg\")]\npublic static string ToolWithIcon(<\/code><\/pre>\nMcpServerResourceTemplateAttribute<\/code>, and McpServerPromptAttribute<\/a>
\nhave also added an IconSource<\/code> parameter.<\/p>\n
\nconfigure icons programmatically via McpServerToolCreateOptions.Icons<\/a>:<\/p>\n.WithTools([\n McpServerTool.Create(\n typeof(EchoTool).GetMethod(nameof(EchoTool.Echo))!,\n options: new McpServerToolCreateOptions\n {\n Icons = [\n new Icon\n {\n Source = \"https:\/\/raw.githubusercontent.com\/microsoft\/fluentui-emoji\/main\/assets\/Loudspeaker\/Flat\/loudspeaker_flat.svg\",\n MimeType = \"image\/svg+xml\",\n Sizes = [\"any\"],\n Theme = \"light\"\n },\n new Icon\n {\n Source = \"https:\/\/raw.githubusercontent.com\/microsoft\/fluentui-emoji\/main\/assets\/Loudspeaker\/3D\/loudspeaker_3d.png\",\n MimeType = \"image\/png\",\n Sizes = [\"256x256\"],\n Theme = \"dark\"\n }\n ]\n }\n )\n])<\/code><\/pre>\n![\"Icons](\"https:\/\/devblogs.microsoft.com\/dotnet\/wp-content\/uploads\/sites\/10\/2026\/03\/icons-for-tools.png\"){kind=icon}
<\/p>\n
\nIcons<\/a> and
\nWebsiteUrl<\/a> properties for server and client metadata:<\/p>\n.AddMcpServer(options =>\n{\n options.ServerInfo = new Implementation\n {\n Name = \"Everything Server\",\n Version = \"1.0.0\",\n Title = \"MCP Everything Server\",\n Description = \"A comprehensive MCP server demonstrating all MCP features\",\n WebsiteUrl = \"https:\/\/github.com\/modelcontextprotocol\/csharp-sdk\",\n Icons = [\n new Icon\n {\n Source = \"https:\/\/raw.githubusercontent.com\/microsoft\/fluentui-emoji\/main\/assets\/Gear\/Flat\/gear_flat.svg\",\n MimeType = \"image\/svg+xml\",\n Sizes = [\"any\"],\n Theme = \"light\"\n }\n ]\n };\n})<\/code><\/pre>\nIncremental scope consent<\/h2>\n
\nto MCP authorization, allowing clients to request only the minimum access needed for each operation.<\/p>\n
\nPreviously, clients might request all possible scopes up front because they couldn\u2019t know which scopes
\na specific operation would require. With incremental scope consent, clients start with minimal scopes
\nand request additional ones as needed.<\/p>\n\n
\n401 Unauthorized<\/code> and a WWW-Authenticate<\/code> header that now includes a scopes<\/code> parameter listing
\nthe scopes needed for the operation. Clients request authorization for only these scopes.<\/p>\n<\/li>\n
\nresponds with 403 Forbidden<\/code> and a WWW-Authenticate<\/code> header containing an error<\/code> parameter
\nof insufficient_scope<\/code> and a scopes<\/code> parameter with the required scopes. The client then
\nobtains a new token with the expanded scopes and retries.<\/p>\n<\/li>\n<\/ul>\nClient support for incremental scope consent<\/h3>\n
401<\/code> or 403<\/code> with a scopes<\/code>
\nparameter in the WWW-Authenticate<\/code> header, it extracts the required scopes and initiates the
\nauthorization flow \u2014 no additional client code needed.<\/p>\nServer support for incremental scope consent<\/h3>\n
\n
builder.Services.AddAuthentication(options =>\n{\n options.DefaultAuthenticateScheme = McpAuthenticationDefaults.AuthenticationScheme;\n options.DefaultChallengeScheme = McpAuthenticationDefaults.AuthenticationScheme;\n})<\/code><\/pre>\n<\/li>\n.AddJwtBearer(options =>\n{\n options.TokenValidationParameters = new TokenValidationParameters\n {\n ValidateIssuer = true,\n ValidateAudience = true,\n ValidateLifetime = true,\n ValidateIssuerSigningKey = true,\n \/\/ Other validation settings as appropriate\n };\n})<\/code><\/pre>\n