docs(stdio): route server diagnostics to stderr

README.md

@@ -26,6 +26,7 @@ package main
 import (
     "context"
     "fmt"
+    "os"
 
     "github.com/mark3labs/mcp-go/mcp"
     "github.com/mark3labs/mcp-go/server"
@@ -53,7 +54,7 @@ func main() {
 
     // Start the stdio server
     if err := server.ServeStdio(s); err != nil {
-        fmt.Printf("Server error: %v\n", err)
+        fmt.Fprintf(os.Stderr, "Server error: %v\n", err)
     }
 }
 
@@ -121,6 +122,7 @@ package main
 import (
     "context"
     "fmt"
+    "os"
 
     "github.com/mark3labs/mcp-go/mcp"
     "github.com/mark3labs/mcp-go/server"
@@ -191,7 +193,7 @@ func main() {
 
     // Start the server
     if err := server.ServeStdio(s); err != nil {
-        fmt.Printf("Server error: %v\n", err)
+        fmt.Fprintf(os.Stderr, "Server error: %v\n", err)
     }
 }
 ```

examples/roots_server/main.go

@@ -4,14 +4,15 @@ import (
 	"context"
 	"fmt"
 	"log"
+	"os"
 
 	"github.com/mark3labs/mcp-go/mcp"
 	"github.com/mark3labs/mcp-go/server"
 )
 
 // handleNotification handles JSON-RPC notifications by printing the notification method to standard output.
 func handleNotification(ctx context.Context, notification mcp.JSONRPCNotification) {
-	fmt.Printf("notification received: %v\n", notification.Method)
+	fmt.Fprintf(os.Stderr, "notification received: %v\n", notification.Method)
 }
 
 // main sets up and runs an MCP stdio server named "roots-stdio-server" with tool and roots capabilities.

examples/structured_input_and_output/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"fmt"
+	"os"
 	"time"
 
 	"github.com/mark3labs/mcp-go/mcp"
@@ -86,7 +87,7 @@ func main() {
 	s.AddTool(manualTool, mcp.NewTypedToolHandler(manualWeatherHandler))
 
 	if err := server.ServeStdio(s); err != nil {
-		fmt.Printf("Server error: %v\n", err)
+		fmt.Fprintf(os.Stderr, "Server error: %v\n", err)
 	}
 }
 

examples/typed_tools/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"fmt"
+	"os"
 
 	"github.com/mark3labs/mcp-go/mcp"
 	"github.com/mark3labs/mcp-go/server"
@@ -76,7 +77,7 @@ func main() {
 
 	// Start the stdio server
 	if err := server.ServeStdio(s); err != nil {
-		fmt.Printf("Server error: %v\n", err)
+		fmt.Fprintf(os.Stderr, "Server error: %v\n", err)
 	}
 }
 

www/docs/pages/getting-started.mdx

@@ -42,6 +42,7 @@ package main
 import (
     "context"
     "fmt"
+    "os"
 
     "github.com/mark3labs/mcp-go/mcp"
     "github.com/mark3labs/mcp-go/server"
@@ -69,7 +70,7 @@ func main() {
 
     // Start the stdio server
     if err := server.ServeStdio(s); err != nil {
-        fmt.Printf("Server error: %v\n", err)
+        fmt.Fprintf(os.Stderr, "Server error: %v\n", err)
     }
 }
 

www/docs/pages/quick-start.mdx

@@ -12,6 +12,7 @@ package main
 import (
     "context"
     "fmt"
+    "os"
 
     "github.com/mark3labs/mcp-go/mcp"
     "github.com/mark3labs/mcp-go/server"
@@ -39,7 +40,7 @@ func main() {
 
     // Start the stdio server
     if err := server.ServeStdio(s); err != nil {
-        fmt.Printf("Server error: %v\n", err)
+        fmt.Fprintf(os.Stderr, "Server error: %v\n", err)
     }
 }
 

www/docs/pages/servers/advanced.mdx

@@ -819,7 +819,7 @@ func (n *CustomNotifier) BroadcastSystemMessage(message string) {
 ```go
 func main() {
     // Initialize components
-    logger := log.New(os.Stdout, "[MCP] ", log.LstdFlags)
+    logger := log.New(os.Stderr, "[MCP] ", log.LstdFlags)
     metrics := NewPrometheusMetrics()
     sessionManager := NewSessionManager()
     notifier := NewCustomNotifier()
@@ -925,7 +925,7 @@ func handleCalculate(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToo
 	if clientSession, ok := session.(server.SessionWithClientInfo); ok {
              clientCapabilities := clientSession.GetClientCapabilities()
 			 if clientCapabilities.Sampling == nil {
-				 fmt.Println("sampling is not enabled in client")
+                 fmt.Fprintln(os.Stderr, "sampling is not enabled in client")
 			 }
 	}
 

www/docs/pages/servers/index.mdx

@@ -28,6 +28,7 @@ import (
     "context"
     "encoding/json"
     "fmt"
+    "os"
     "time"
 
     "github.com/mark3labs/mcp-go/mcp"
@@ -83,7 +84,7 @@ func main() {
 
     // Start the server
     if err := server.ServeStdio(s); err != nil {
-        fmt.Printf("Server error: %v\n", err)
+        fmt.Fprintf(os.Stderr, "Server error: %v\n", err)
     }
 }
 

www/docs/pages/transports/index.mdx

@@ -70,7 +70,7 @@ func main() {
         httpServer := server.NewStreamableHTTPServer(s)
         httpServer.Start(":" + port)
     default:
-        fmt.Println("Starting STDIO server")
+        fmt.Fprintln(os.Stderr, "Starting STDIO server")
         server.ServeStdio(s)
     }
 }