McpSdk.Adapter.System.Text.Json 1.0.0

McpSdk

A lean, zero-dependency C# SDK for the Model Context Protocol. It implements the 2025-11-25 revision and negotiates down to older peers (2025-06-18, 2025-03-26, 2024-11-05). Both client and server ship from this repo, over stdio or Streamable HTTP.

Capability & feature matrix

Reflects what the code actually serves as of the 2025-11-25 revision. ✅ supported · ❌ not implemented (by deliberate scope choice).

Protocol & transport

Server — methods served

Server-emitted notifications: notifications/message, notifications/progress, notifications/cancelled, notifications/tools/list_changed, notifications/prompts/list_changed, notifications/resources/list_changed, notifications/resources/updated.

Client — server→client requests handled

The client surfaces inbound notifications/message as LogMessageReceived and notifications/progress as ProgressReceived.

Tools & content features

Examples

Client Example

using McpSdk.Adapter.Newtonsoft.Json;
using McpSdk.Client;
using McpSdk.Protocol;

var json = new NewtonsoftJson();
var rootsCapabilityFactory = new RootsCapabilityFactory(json);
var samplingCapabilityFactory = new SamplingCapabilityFactory(json);

var client = new ClientBuilder(json)
    .WithName("Echo Client")
    .WithVersion("1.0.0")
    .WithStdioTransport("bun", ["index.ts"])
    .WithRootsCapability(rootsCapabilityFactory)
    .WithSamplingCapability(samplingCapabilityFactory)
    .Build();

await client.Connect();

Server Example

using McpSdk.Adapter.ConsoleLogger;
using McpSdk.Adapter.Newtonsoft.Json;
using McpSdk.Server;
using McpSdk.Server.Tests;

var json = new NewtonsoftJson();
var mcpServer = new ServerBuilder()
    .WithName("Demo Server")
    .WithVersion("1.0.0")
    .WithConsoleLogger()
    .WithStdioTransport(json)
    .WithDefaultToolsCapability(json, tools =>
    {
        tools.AddTool(new TestTool());
    })
    .Build();

await mcpServer.Start();

Streamable HTTP (2025-11-25)

A single MCP endpoint over HTTP. The listener issues an Mcp-Session-Id on initialize and serves one McpServer per session; subsequent requests carry that id and the MCP-Protocol-Version header. Disallowed Origins are rejected with 403, and the server→client GET stream supports Last-Event-ID resumption.

// Server
using McpSdk.Adapter.ConsoleLogger;
using McpSdk.Adapter.Newtonsoft.Json;
using McpSdk.Adapter.StreamableHttpServer;
using McpSdk.Server;

var json = new NewtonsoftJson();
var loggerFactory = new ServerConsoleLoggerFactory();
var listener = new StreamableHttpListener(
    "http://localhost:3000", "/mcp", json, loggerFactory,
    onSession: async transport =>
    {
        var server = new ServerBuilder()
            .WithName("Demo Server")
            .WithVersion("1.0.0")
            .WithLogger(loggerFactory)
            .WithStreamableHttpTransport(transport)
            .WithDefaultToolsCapability(json, tools => tools.AddTool(new TestTool()))
            .Build();
        await server.Start();
    });

await listener.Start();

// Client
using McpSdk.Adapter.ConsoleLogger;
using McpSdk.Adapter.Newtonsoft.Json;
using McpSdk.Adapter.System.Net.Http;
using McpSdk.Client;

var json = new NewtonsoftJson();
var loggerFactory = new ClientConsoleLoggerFactory();
var http = new StreamableHttpClientAdapter("http://localhost:3000/mcp", loggerFactory);

var client = new ClientBuilder()
    .WithName("Echo Client")
    .WithVersion("1.0.0")
    .WithLogger(loggerFactory)
    .WithStreamableHttpTransport(json, http)
    .Build();

await client.Connect();

License

Licensed under the MIT License.