modelcontextprotocol · findleyr · Nov 12, 2025 · Oct 11, 2025 · Oct 11, 2025 · Oct 19, 2025
diff --git a/mcp/conformance_test.go b/mcp/conformance_test.go
@@ -135,19 +135,36 @@ func incTool(_ context.Context, _ *CallToolRequest, args incInput) (*CallToolRes
 	return nil, incOutput{args.X + 1}, nil
 }
 
+var iconObj = Icon{Source: "data:image/png;base64,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",
+	MIMEType: "image/png", Sizes: []string{"48x48", "96x96"}}
+
 // runServerTest runs the server conformance test.
 // It must be executed in a synctest bubble.
 func runServerTest(t *testing.T, test *conformanceTest) {
 	ctx := t.Context()
 	// Construct the server based on features listed in the test.
-	s := NewServer(&Implementation{Name: "testServer", Version: "v1.0.0"}, nil)
+	impl := &Implementation{Name: "testServer", Version: "v1.0.0"}
+
+	// TODO(IAmSurajBobade): Remove this hack once we have a client protocol specific handling.
+	if test.name == "version-draft.txtar" {
+		impl.Icons = []Icon{iconObj}
+		impl.WebsiteURL = "https://modelcontextprotocol.io"
+	}
+
+	s := NewServer(impl, nil)
 	for _, tn := range test.tools {
 		switch tn {
 		case "greet":
 			AddTool(s, &Tool{
 				Name:        "greet",
 				Description: "say hi",
 			}, sayHi)
+		case "greetWithIcon":
+			AddTool(s, &Tool{
+				Name:        "greetWithIcon",
+				Description: "say hi",
+				Icons:       []Icon{iconObj},
+			}, sayHi)
 		case "structured":
 			AddTool(s, &Tool{Name: "structured"}, structuredTool)
 		case "tomorrow":
@@ -167,6 +184,13 @@ func runServerTest(t *testing.T, test *conformanceTest) {
 		switch pn {
 		case "code_review":
 			s.AddPrompt(codeReviewPrompt, codReviewPromptHandler)
+		case "code_reviewWithIcon":
+			s.AddPrompt(&Prompt{
+				Name:        "code_review",
+				Description: "do a code review",
+				Arguments:   []*PromptArgument{{Name: "Code", Required: true}},
+				Icons:       []Icon{iconObj},
+			}, codReviewPromptHandler)
 		default:
 			t.Fatalf("unknown prompt %q", pn)
 		}
@@ -177,6 +201,13 @@ func runServerTest(t *testing.T, test *conformanceTest) {
 			s.AddResource(resource1, readHandler)
 		case "info":
 			s.AddResource(resource3, handleEmbeddedResource)
+		case "infoWithIcon":
+			s.AddResource(&Resource{
+				Name:     "info",
+				MIMEType: "text/plain",
+				URI:      "embedded:info",
+				Icons:    []Icon{iconObj},
+			}, handleEmbeddedResource)
 		default:
 			t.Fatalf("unknown resource %q", rn)
 		}

diff --git a/mcp/protocol.go b/mcp/protocol.go
@@ -658,6 +658,21 @@ type ProgressNotificationParams struct {
 
 func (*ProgressNotificationParams) isParams() {}
 
+// Icon provides visual identifiers for their resources, tools, prompts, and implementations
+// See [/specification/draft/basic/index#icons] for notes on icons
+
+// TODO(iamsurajbobade): update specification url from draft.
+type Icon struct {
+	// Source is A URI pointing to the icon resource (required). This can be:
+	// - An HTTP/HTTPS URL pointing to an image file
+	// - A data URI with base64-encoded image data
+	Source string `json:"src"`
+	// Optional MIME type if the server's type is missing or generic
+	MIMEType string `json:"mimeType,omitempty"`
+	// Optional size specification (e.g., ["48x48"], ["any"] for scalable formats like SVG, or ["48x48", "96x96"] for multiple sizes)
+	Sizes []string `json:"sizes,omitempty"`
+}
+
 // A prompt or prompt template that the server offers.
 type Prompt struct {
 	// See [specification/2025-06-18/basic/index#general-fields] for notes on _meta
@@ -673,6 +688,8 @@ type Prompt struct {
 	// Intended for UI and end-user contexts — optimized to be human-readable and
 	// easily understood, even by those unfamiliar with domain-specific terminology.
 	Title string `json:"title,omitempty"`
+	// Icons for the prompt, if any.
+	Icons []Icon `json:"icons,omitempty"`
 }
 
 // Describes an argument that a prompt can accept.
@@ -782,6 +799,8 @@ type Resource struct {
 	Title string `json:"title,omitempty"`
 	// The URI of this resource.
 	URI string `json:"uri"`
+	// Icons for the resource, if any.
+	Icons []Icon `json:"icons,omitempty"`
 }
 
 type ResourceListChangedParams struct {
@@ -948,6 +967,8 @@ type Tool struct {
 	// If not provided, Annotations.Title should be used for display if present,
 	// otherwise Name.
 	Title string `json:"title,omitempty"`
+	// Icons for the tool, if any.
+	Icons []Icon `json:"icons,omitempty"`
 }
 
 // Additional properties describing a Tool to clients.
@@ -1090,6 +1111,10 @@ type Implementation struct {
 	// easily understood, even by those unfamiliar with domain-specific terminology.
 	Title   string `json:"title,omitempty"`
 	Version string `json:"version"`
+	// WebsiteURL for the server, if any.
+	WebsiteURL string `json:"websiteUrl,omitempty"`
+	// Icons for the Server, if any.
+	Icons []Icon `json:"icons,omitempty"`
 }
 
 // Present if the server supports argument autocompletion suggestions.

diff --git a/mcp/shared.go b/mcp/shared.go
@@ -33,8 +33,10 @@ const (
 	//
 	// It is the version that the client sends in the initialization request, and
 	// the default version used by the server.
-	latestProtocolVersion   = protocolVersion20250618
-	protocolVersion20250618 = "2025-06-18"
+	latestProtocolVersion = protocolVersion20250618
+
+	protocolVersionDraft    = "draft"      // draft protocol version with experimental features for testing
+	protocolVersion20250618 = "2025-06-18" // latest stable version
 	protocolVersion20250326 = "2025-03-26"
 	protocolVersion20241105 = "2024-11-05"
 )
@@ -48,6 +50,12 @@ var supportedProtocolVersions = []string{
 // negotiatedVersion returns the effective protocol version to use, given a
 // client version.
 func negotiatedVersion(clientVersion string) string {
+	// If client sends protocol version draft, enable draft features.
+	if clientVersion == protocolVersionDraft {
+		log.Printf("Using draft protocol version features")
+		return protocolVersionDraft
+	}
+
 	// In general, prefer to use the clientVersion, but if we don't support the
 	// client's version, use the latest version.
 	//