The Model Context Protocol allows clients to get notified when a resource has changed. This allows clients to do things like refresh the LLMs context when an underlying resource has changed. Lets say you have some application logs in a resource, the server could periodically refresh the application log resource to allow the client to get latest logs.

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Implementation

In mcp-golang, the server will send a notification to the client when any of the following events occur:

  • A new tool is registered via the RegisterTool function
  • A new prompt is registered via the RegisterPrompt function
  • A new resource is registered via the RegisterResource function
  • A prompt is deregistered via the DeregisterPrompt function
  • A tool is deregistered via the DeregisterTool function
  • A resource is deregistered via the DeregisterResource function

A silly e2e example of this is the server below. It registers and deregisters a tool, prompt, and resource every second causing 3 notifications to be sent to the client each second.

package main

import (
	"fmt"
	mcp_golang "github.com/metoro-io/mcp-golang"
	"github.com/metoro-io/mcp-golang/transport/stdio"
	"time"
)

type HelloArguments struct {
	Submitter string `json:"submitter" jsonschema:"required,description=The name of the thing calling this tool (openai or google or claude etc)'"`
}

type Content struct {
	Title       string  `json:"title" jsonschema:"required,description=The title to submit"`
	Description *string `json:"description" jsonschema:"description=The description to submit"`
}

func main() {
	done := make(chan struct{})
	server := mcp_golang.NewServer(stdio.NewStdioServerTransport())
	err := server.Serve()
	if err != nil {
		panic(err)
	}
	go func() {
		for {
			err := server.RegisterTool("hello", "Say hello to a person", func(arguments HelloArguments) (*mcp_golang.ToolResponse, error) {
				return mcp_golang.NewToolResponse(mcp_golang.NewTextContent(fmt.Sprintf("Hello, %s!", arguments.Submitter))), nil
			})
			if err != nil {
				panic(err)
			}
			time.Sleep(1 * time.Second)
			err = server.DeregisterTool("hello")
			if err != nil {
				panic(err)
			}
		}
	}()
	go func() {
		for {

			err = server.RegisterPrompt("prompt_test", "This is a test prompt", func(arguments Content) (*mcp_golang.PromptResponse, error) {
				return mcp_golang.NewPromptResponse("description", mcp_golang.NewPromptMessage(mcp_golang.NewTextContent(fmt.Sprintf("Hello, %server!", arguments.Title)), mcp_golang.RoleUser)), nil
			})
			if err != nil {
				panic(err)
			}
			time.Sleep(1 * time.Second)
			err = server.DeregisterPrompt("prompt_test")
			if err != nil {
				panic(err)
			}
		}

	}()
	go func() {
		err = server.RegisterResource("test://resource", "resource_test", "This is a test resource", "application/json", func() (*mcp_golang.ResourceResponse, error) {
			return mcp_golang.NewResourceResponse(mcp_golang.NewTextEmbeddedResource("test://resource", "This is a test resource", "application/json")), nil
		})
		if err != nil {
			panic(err)
		}
		time.Sleep(1 * time.Second)
		err = server.DeregisterResource("test://resource")
		if err != nil {
			panic(err)
		}
	}()

	<-done
}