change to strong content type

client/sse.go

@@ -462,12 +462,7 @@ func (c *SSEMCPClient) GetPrompt(
 		return nil, err
 	}
 
-	var result mcp.GetPromptResult
-	if err := json.Unmarshal(*response, &result); err != nil {
-		return nil, fmt.Errorf("failed to unmarshal response: %w", err)
-	}
-
-	return &result, nil
+	return mcp.ParseGetPromptResult(response)
 }
 
 func (c *SSEMCPClient) ListTools(
@@ -496,12 +491,7 @@ func (c *SSEMCPClient) CallTool(
 		return nil, err
 	}
 
-	var result mcp.CallToolResult
-	if err := json.Unmarshal(*response, &result); err != nil {
-		return nil, fmt.Errorf("failed to unmarshal response: %w", err)
-	}
-
-	return &result, nil
+	return mcp.ParseCallToolResult(response)
 }
 
 func (c *SSEMCPClient) SetLevel(

client/sse_test.go

@@ -25,7 +25,7 @@ func TestSSEMCPClient(t *testing.T) {
 		mcp.WithString("parameter-1", mcp.Description("A string tool parameter")),
 	), func(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
 		return &mcp.CallToolResult{
-			Content: []interface{}{
+			Content: []mcp.Content{
 				mcp.TextContent{
 					Type: "text",
 					Text: "Input parameter: " + request.Params.Arguments["parameter-1"].(string),

client/stdio.go

@@ -388,12 +388,7 @@ func (c *StdioMCPClient) GetPrompt(
 		return nil, err
 	}
 
-	var result mcp.GetPromptResult
-	if err := json.Unmarshal(*response, &result); err != nil {
-		return nil, fmt.Errorf("failed to unmarshal response: %w", err)
-	}
-
-	return &result, nil
+	return mcp.ParseGetPromptResult(response)
 }
 
 func (c *StdioMCPClient) ListTools(
@@ -422,12 +417,7 @@ func (c *StdioMCPClient) CallTool(
 		return nil, err
 	}
 
-	var result mcp.CallToolResult
-	if err := json.Unmarshal(*response, &result); err != nil {
-		return nil, fmt.Errorf("failed to unmarshal response: %w", err)
-	}
-
-	return &result, nil
+	return mcp.ParseCallToolResult(response)
 }
 
 func (c *StdioMCPClient) SetLevel(

examples/everything/main.go

@@ -280,7 +280,7 @@ func (s *MCPServer) handleEchoTool(
 		return nil, fmt.Errorf("invalid message argument")
 	}
 	return &mcp.CallToolResult{
-		Content: []interface{}{
+		Content: []mcp.Content{
 			mcp.TextContent{
 				Type: "text",
 				Text: fmt.Sprintf("Echo: %s", message),
@@ -301,7 +301,7 @@ func (s *MCPServer) handleAddTool(
 	}
 	sum := a + b
 	return &mcp.CallToolResult{
-		Content: []interface{}{
+		Content: []mcp.Content{
 			mcp.TextContent{
 				Type: "text",
 				Text: fmt.Sprintf("The sum of %f and %f is %f.", a, b, sum),
@@ -330,7 +330,7 @@ func (s *MCPServer) handleSendNotification(
 	}
 
 	return &mcp.CallToolResult{
-		Content: []interface{}{
+		Content: []mcp.Content{
 			mcp.TextContent{
 				Type: "text",
 				Text: "notification sent successfully",
@@ -373,7 +373,7 @@ func (s *MCPServer) handleLongRunningOperationTool(
 	}
 
 	return &mcp.CallToolResult{
-		Content: []interface{}{
+		Content: []mcp.Content{
 			mcp.TextContent{
 				Type: "text",
 				Text: fmt.Sprintf(
@@ -412,7 +412,7 @@ func (s *MCPServer) handleGetTinyImageTool(
 	request mcp.CallToolRequest,
 ) (*mcp.CallToolResult, error) {
 	return &mcp.CallToolResult{
-		Content: []interface{}{
+		Content: []mcp.Content{
 			mcp.TextContent{
 				Type: "text",
 				Text: "This is a tiny image:",

mcp/prompts.go

@@ -77,18 +77,8 @@ const (
 // This is similar to `SamplingMessage`, but also supports the embedding of
 // resources from the MCP server.
 type PromptMessage struct {
-	Role    Role        `json:"role"`
-	Content interface{} `json:"content"` // Can be TextContent, ImageContent, or EmbeddedResource
-}
-
-// EmbeddedResource represents the contents of a resource, embedded into a prompt or tool call result.
-//
-// It is up to the client how best to render embedded resources for the
-// benefit of the LLM and/or the user.
-type EmbeddedResource struct {
-	Annotated
-	Type     string           `json:"type"`
-	Resource ResourceContents `json:"resource"`
+	Role    Role    `json:"role"`
+	Content Content `json:"content"` // Can be TextContent, ImageContent, or EmbeddedResource
 }
 
 // PromptListChangedNotification is an optional notification from the server

mcp/tools.go

@@ -25,7 +25,7 @@ type ListToolsResult struct {
 // should be reported as an MCP error response.
 type CallToolResult struct {
 	Result
-	Content []interface{} `json:"content"` // Can be TextContent, ImageContent, or      EmbeddedResource
+	Content []Content `json:"content"` // Can be TextContent, ImageContent, or      EmbeddedResource
 	// Whether the tool call ended in an error.
 	//
 	// If not set, this is assumed to be false (the call was successful).

mcp/types.go

@@ -585,6 +585,10 @@ type Annotated struct {
 	} `json:"annotations,omitempty"`
 }
 
+type Content interface {
+	isContent()
+}
+
 // TextContent represents text provided to or from an LLM.
 // It must have Type set to "text".
 type TextContent struct {
@@ -594,6 +598,8 @@ type TextContent struct {
 	Text string `json:"text"`
 }
 
+func (TextContent) isContent() {}
+
 // ImageContent represents an image provided to or from an LLM.
 // It must have Type set to "image".
 type ImageContent struct {
@@ -605,6 +611,20 @@ type ImageContent struct {
 	MIMEType string `json:"mimeType"`
 }
 
+func (ImageContent) isContent() {}
+
+// EmbeddedResource represents the contents of a resource, embedded into a prompt or tool call result.
+//
+// It is up to the client how best to render embedded resources for the
+// benefit of the LLM and/or the user.
+type EmbeddedResource struct {
+	Annotated
+	Type     string           `json:"type"`
+	Resource ResourceContents `json:"resource"`
+}
+
+func (EmbeddedResource) isContent() {}
+
 // ModelPreferences represents the server's preferences for model selection,
 // requested of the client during sampling.
 //