fix: startup messages to stderr. (reserve stdio for JSON-RPC MCP messages) (#1)

Author: evalstate

cmd/root.go

@@ -38,14 +38,14 @@ func Execute() {
 		log.Fatalf("Invalid config: %v", err)
 	}
 
-	fmt.Printf("Loaded %d server(s):\n", len(cfg.MCPServers))
+	fmt.Fprintf(os.Stderr, "Loaded %d server(s):\n", len(cfg.MCPServers))
 	for name, srv := range cfg.MCPServers {
 		tt, _ := srv.TransportType() // already validated
 		switch tt {
 		case config.TransportSTDIO:
-			fmt.Printf("  [%s] %s → %s %v\n", name, tt, srv.Command, srv.Args)
+			fmt.Fprintf(os.Stderr, "  [%s] %s → %s %v\n", name, tt, srv.Command, srv.Args)
 		case config.TransportHTTP, config.TransportSSE:
-			fmt.Printf("  [%s] %s → %s\n", name, tt, srv.URL)
+			fmt.Fprintf(os.Stderr, "  [%s] %s → %s\n", name, tt, srv.URL)
 		}
 	}
 
@@ -58,7 +58,7 @@ func Execute() {
 	}
 	defer mgr.Close()
 
-	fmt.Printf("Connected to %d skill(s): %v\n", len(mgr.ListServerNames()), mgr.ListServerNames())
+	fmt.Fprintf(os.Stderr, "Connected to %d skill(s): %v\n", len(mgr.ListServerNames()), mgr.ListServerNames())
 
 	s := server.NewServer(mgr)
 	if err := server.Serve(ctx, s, transport, host, port); err != nil {

internal/server/server.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net"
 	"net/http"
+	"os"
 
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 	"skillful-mcp/internal/clientmanager"
@@ -39,7 +40,7 @@ func Serve(ctx context.Context, s *mcp.Server, transport, host, port string) err
 			<-ctx.Done()
 			srv.Close()
 		}()
-		fmt.Printf("Listening on %s\n", addr)
+		fmt.Fprintf(os.Stderr, "Listening on %s\n", addr)
 		if err := srv.ListenAndServe(); err != http.ErrServerClosed {
 			return err
 		}