diff --git a/main.go b/main.go
index 4681b44..100f8d6 100644
--- a/main.go
+++ b/main.go
@@ -11,6 +11,7 @@ import (
 )
 
 type CmdDaemon struct {
+	Name       string // app cli command name
 	SocketPath string // unix socket path
 	cmds       map[string]CmdHandler
 }
@@ -103,7 +104,7 @@ func (c *CmdDaemon) Listen() error {
 			cmdHandler, ok := c.cmds[req.Cmd]
 			if !ok {
 				_ = Write(conn, CmdResponse{
-					Error:    "unknown command: " + req.Cmd,
+					Error:    "unknown command: " + req.Cmd + "\n" + c.Usage(),
 					Continue: false,
 				})
 				return
@@ -113,12 +114,23 @@ func (c *CmdDaemon) Listen() error {
 			cmdConn := &CmdConn{Conn: conn, Id: req.Id}
 			err = cmdHandler.Handle(cmdConn, req)
 			if err != nil {
-				_ = cmdConn.WriteError(err, false)
+				_ = cmdConn.End(err.Error() + cmdHandler.Usage())
 			}
 		}(conn)
 	}
 }
 
+func (c *CmdDaemon) Usage() string {
+	usage := fmt.Sprintf("Usage: %s [options] <command> [args...]\n\n", c.Name)
+	usage += "Options:\n"
+	usage += "  -d, --debug  Run command in debug mode\n\n"
+	usage += "Commands:\n"
+	for cmd, handler := range c.cmds {
+		usage += fmt.Sprintf("  %-10s %s\n", cmd, handler.Description())
+	}
+	return usage
+}
+
 func (c *CmdDaemon) RegisterCmd(cmd string, handler CmdHandler) {
 	c.cmds[cmd] = handler
 }