MCP Go SDK v0.2.0

BREAKING CHANGES

This version contains breaking changes. See the release notes for details.

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

Warning

The SDK should be considered unreleased, and is currently unstable and subject to breaking changes. Please test it out and file bug reports or API proposals, but don't use it in real projects. See the issue tracker for known issues and missing features. We aim to release a stable version of the SDK in August, 2025.

Design

The design doc for this SDK is at design.md, which was initially reviewed at modelcontextprotocol/discussions/364.

Further design discussion should occur in issues (for concrete proposals) or discussions for open-ended discussion. See CONTRIBUTING.md for details.

Package documentation

The SDK consists of three 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/jsonschema package provides an implementation of JSON Schema, used for MCP tool input and output schema.
• The github.com/modelcontextprotocol/go-sdk/jsonrpc package is for users implementing their own transports.

Example

In this example, an MCP client communicates with an MCP server running in a sidecar process:

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)
	}
}

Here's an example of the corresponding server component, which communicates with its client over stdin/stdout:

package main

import (
	"context"
	"log"

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

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

func SayHi(ctx context.Context, req *mcp.ServerRequest[*mcp.CallToolParams], args HiParams) (*mcp.CallToolResult, any, error) {
	return &mcp.CallToolResult{
		Content: []mcp.Content{&mcp.TextContent{Text: "Hi " + args.Name}},
	}, nil, 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)
	}
}

The examples/ directory contains more example clients and servers.

Acknowledgements

Several existing Go MCP SDKs inspired the development and design of this official SDK, notably mcp-go, 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 the MIT License - see the LICENSE file for details.