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MCP Go SDK

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 two 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.

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-client", "v1.0.0", nil)

 // Connect to a server over stdin/stdout
 transport := mcp.NewCommandTransport(exec.Command("myserver"))
 session, err := client.Connect(ctx, transport)
 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"`
}

func SayHi(ctx context.Context, cc *mcp.ServerSession, params *mcp.CallToolParamsFor[HiParams]) (*mcp.CallToolResultFor[any], error) {
 return &mcp.CallToolResultFor[any]{
 Content: []mcp.Content{&mcp.TextContent{Text: "Hi " + params.Arguments.Name}},
 }, nil
}

func main() {
 // Create a server with a single tool.
 server := mcp.NewServer("greeter", "v1.0.0", nil)
 server.AddTools(
 mcp.NewServerTool("greet", "say hi", SayHi, mcp.Input(
 mcp.Property("name", mcp.Description("the name of the person to greet")),
 )),
 )
 // Run the server over stdin/stdout, until the client disconnects
 if err := server.Run(context.Background(), mcp.NewStdioTransport()); 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.