MCP Go SDK

This repository contains an implementation of the official Go software development kit (SDK) for the Model Context Protocol (MCP).

Package / Feature documentation

The SDK consists of several importable packages:

• The github.com/modelcontextprotocol/go-sdk/mcp package defines the primary APIs for constructing and using MCP clients and servers.
• The github.com/modelcontextprotocol/go-sdk/jsonrpc package is for users implementing their own transports.
• The github.com/modelcontextprotocol/go-sdk/auth package provides some primitives for supporting OAuth.
• The github.com/modelcontextprotocol/go-sdk/oauthex package provides extensions to the OAuth protocol, such as ProtectedResourceMetadata.

The SDK endeavors to implement the full MCP spec. The docs/ directory contains feature documentation, mapping the MCP spec to the packages above.

Version Compatibility

The following table shows which versions of the Go SDK support which versions of the MCP specification:

* Client side OAuth has experimental support.

** Partial support for 2025-11-25 (client side OAuth and Sampling with tools not available).

New releases of the SDK target only supported versions of Go. See https://go.dev/doc/devel/release#policy for more information.

Getting started

To get started creating an MCP server, create an mcp.Server instance, add features to it, and then run it over an mcp.Transport. For example, this server adds a single simple tool, and then connects it to clients over stdin/stdout:

package main

import (
    "context"
    "log"

    "github.com/modelcontextprotocol/go-sdk/mcp"
)

type Input struct {
    Name string `json:"name" jsonschema:"the name of the person to greet"`
}

type Output struct {
    Greeting string `json:"greeting" jsonschema:"the greeting to tell to the user"`
}

func SayHi(ctx context.Context, req *mcp.CallToolRequest, input Input) (
    *mcp.CallToolResult,
    Output,
    error,
) {
    return nil, Output{Greeting: "Hi " + input.Name}, nil
}

func main() {
    // Create a server with a single tool.
    server := mcp.NewServer(&mcp.Implementation{Name: "greeter", Version: "v1.0.0"}, nil)
    mcp.AddTool(server, &mcp.Tool{Name: "greet", Description: "say hi"}, SayHi)
    // Run the server over stdin/stdout, until the client disconnects.
    if err := server.Run(context.Background(), &mcp.StdioTransport{}); err != nil {
        log.Fatal(err)
    }
}

To communicate with that server, create an mcp.Client and connect it to the corresponding server, by running the server command and communicating over its stdin/stdout:

package main

import (
    "context"
    "log"
    "os/exec"

    "github.com/modelcontextprotocol/go-sdk/mcp"
)

func main() {
    ctx := context.Background()

    // Create a new client, with no features.
    client := mcp.NewClient(&mcp.Implementation{Name: "mcp-client", Version: "v1.0.0"}, nil)

    // Connect to a server over stdin/stdout.
    transport := &mcp.CommandTransport{Command: exec.Command("myserver")}
    session, err := client.Connect(ctx, transport, nil)
    if err != nil {
        log.Fatal(err)
    }
    defer session.Close()

    // Call a tool on the server.
    params := &mcp.CallToolParams{
        Name:      "greet",
        Arguments: map[string]any{"name": "you"},
    }
    res, err := session.CallTool(ctx, params)
    if err != nil {
        log.Fatalf("CallTool failed: %v", err)
    }
    if res.IsError {
        log.Fatal("tool failed")
    }
    for _, c := range res.Content {
        log.Print(c.(*mcp.TextContent).Text)
    }
}

The examples/ directory contains more example clients and servers.

Contributing

We welcome contributions to the SDK! Please see CONTRIBUTING.md for details of how to contribute.

Acknowledgements / Alternatives

Several third party Go MCP SDKs inspired the development and design of this official SDK, and continue to be viable alternatives, notably mcp-go, originally authored by Ed Zynda. We are grateful to Ed as well as the other contributors to mcp-go, and to authors and contributors of other SDKs such as mcp-golang and go-mcp. Thanks to their work, there is a thriving ecosystem of Go MCP clients and servers.

License

This project is licensed under Apache 2.0 for new contributions, with existing code under MIT - see the LICENSE file for details.