go-sdk/examples/server/everything/main.go

// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.

// The everything server implements all supported features of an MCP server.
package main

import (
	"context"
	"flag"
	"fmt"
	"log"
	"net/http"
	"net/url"
	"os"
	"strings"

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

var httpAddr = flag.String("http", "", "if set, use streamable HTTP at this address, instead of stdin/stdout")

func main() {
	flag.Parse()

	opts := &mcp.ServerOptions{
		Instructions:      "Use this server!",
		CompletionHandler: complete, // support completions by setting this handler
	}

	server := mcp.NewServer(&mcp.Implementation{Name: "everything"}, opts)

	// Add tools that exercise different features of the protocol.
	mcp.AddTool(server, &mcp.Tool{Name: "greet", Description: "say hi"}, contentTool)
	mcp.AddTool(server, &mcp.Tool{Name: "greet (structured)"}, structuredTool) // returns structured output
	mcp.AddTool(server, &mcp.Tool{Name: "ping"}, pingingTool)                  // performs a ping
	mcp.AddTool(server, &mcp.Tool{Name: "log"}, loggingTool)                   // performs a log
	mcp.AddTool(server, &mcp.Tool{Name: "sample"}, samplingTool)               // performs sampling
	mcp.AddTool(server, &mcp.Tool{Name: "elicit"}, elicitingTool)              // performs elicitation
	mcp.AddTool(server, &mcp.Tool{Name: "roots"}, rootsTool)                   // lists roots

	// Add a basic prompt.
	server.AddPrompt(&mcp.Prompt{Name: "greet"}, prompt)

	// Add an embedded resource.
	server.AddResource(&mcp.Resource{
		Name:     "info",
		MIMEType: "text/plain",
		URI:      "embedded:info",
	}, embeddedResource)

	// Serve over stdio, or streamable HTTP if -http is set.
	if *httpAddr != "" {
		handler := mcp.NewStreamableHTTPHandler(func(*http.Request) *mcp.Server {
			return server
		}, nil)
		log.Printf("MCP handler listening at %s", *httpAddr)
		http.ListenAndServe(*httpAddr, handler)
	} else {
		t := &mcp.LoggingTransport{Transport: &mcp.StdioTransport{}, Writer: os.Stderr}
		if err := server.Run(context.Background(), t); err != nil {
			log.Printf("Server failed: %v", err)
		}
	}
}

func prompt(ctx context.Context, req *mcp.GetPromptRequest) (*mcp.GetPromptResult, error) {
	return &mcp.GetPromptResult{
		Description: "Hi prompt",
		Messages: []*mcp.PromptMessage{
			{
				Role:    "user",
				Content: &mcp.TextContent{Text: "Say hi to " + req.Params.Arguments["name"]},
			},
		},
	}, nil
}

var embeddedResources = map[string]string{
	"info": "This is the hello example server.",
}

func embeddedResource(_ context.Context, req *mcp.ReadResourceRequest) (*mcp.ReadResourceResult, error) {
	u, err := url.Parse(req.Params.URI)
	if err != nil {
		return nil, err
	}
	if u.Scheme != "embedded" {
		return nil, fmt.Errorf("wrong scheme: %q", u.Scheme)
	}
	key := u.Opaque
	text, ok := embeddedResources[key]
	if !ok {
		return nil, fmt.Errorf("no embedded resource named %q", key)
	}
	return &mcp.ReadResourceResult{
		Contents: []*mcp.ResourceContents{
			{URI: req.Params.URI, MIMEType: "text/plain", Text: text},
		},
	}, nil
}

type args struct {
	Name string `json:"name" jsonschema:"the name to say hi to"`
}

// contentTool is a tool that returns unstructured content.
//
// Since its output type is 'any', no output schema is created.
func contentTool(ctx context.Context, req *mcp.CallToolRequest, args args) (*mcp.CallToolResult, any, error) {
	return &mcp.CallToolResult{
		Content: []mcp.Content{
			&mcp.TextContent{Text: "Hi " + args.Name},
		},
	}, nil, nil
}

type result struct {
	Message string `json:"message" jsonschema:"the message to convey"`
}

// structuredTool returns a structured result.
func structuredTool(ctx context.Context, req *mcp.CallToolRequest, args *args) (*mcp.CallToolResult, *result, error) {
	return nil, &result{Message: "Hi " + args.Name}, nil
}

func pingingTool(ctx context.Context, req *mcp.CallToolRequest, _ any) (*mcp.CallToolResult, any, error) {
	if err := req.Session.Ping(ctx, nil); err != nil {
		return nil, nil, fmt.Errorf("ping failed")
	}
	return nil, nil, nil
}

func loggingTool(ctx context.Context, req *mcp.CallToolRequest, _ any) (*mcp.CallToolResult, any, error) {
	if err := req.Session.Log(ctx, &mcp.LoggingMessageParams{
		Data:  "something happened!",
		Level: "error",
	}); err != nil {
		return nil, nil, fmt.Errorf("log failed")
	}
	return nil, nil, nil
}

func rootsTool(ctx context.Context, req *mcp.CallToolRequest, _ any) (*mcp.CallToolResult, any, error) {
	res, err := req.Session.ListRoots(ctx, nil)
	if err != nil {
		return nil, nil, fmt.Errorf("listing roots failed: %v", err)
	}
	var allroots []string
	for _, r := range res.Roots {
		allroots = append(allroots, fmt.Sprintf("%s:%s", r.Name, r.URI))
	}
	return &mcp.CallToolResult{
		Content: []mcp.Content{
			&mcp.TextContent{Text: strings.Join(allroots, ",")},
		},
	}, nil, nil
}

func samplingTool(ctx context.Context, req *mcp.CallToolRequest, _ any) (*mcp.CallToolResult, any, error) {
	res, err := req.Session.CreateMessage(ctx, new(mcp.CreateMessageParams))
	if err != nil {
		return nil, nil, fmt.Errorf("sampling failed: %v", err)
	}
	return &mcp.CallToolResult{
		Content: []mcp.Content{
			res.Content,
		},
	}, nil, nil
}

func elicitingTool(ctx context.Context, req *mcp.CallToolRequest, _ any) (*mcp.CallToolResult, any, error) {
	res, err := req.Session.Elicit(ctx, &mcp.ElicitParams{
		Message: "provide a random string",
		RequestedSchema: &jsonschema.Schema{
			Type: "object",
			Properties: map[string]*jsonschema.Schema{
				"random": {Type: "string"},
			},
		},
	})
	if err != nil {
		return nil, nil, fmt.Errorf("eliciting failed: %v", err)
	}
	return &mcp.CallToolResult{
		Content: []mcp.Content{
			&mcp.TextContent{Text: res.Content["random"].(string)},
		},
	}, nil, nil
}

func complete(ctx context.Context, req *mcp.CompleteRequest) (*mcp.CompleteResult, error) {
	return &mcp.CompleteResult{
		Completion: mcp.CompletionResultDetails{
			Total:  1,
			Values: []string{req.Params.Argument.Value + "x"},
		},
	}, nil
}