diff --git a/cmd/contacts.go b/cmd/contacts.go
index 4245141..82c765b 100644
--- a/cmd/contacts.go
+++ b/cmd/contacts.go
@@ -104,10 +104,6 @@ var contactsFindCmd = &cobra.Command{
 		email, _ := cmd.Flags().GetString("email")
 		userID, _ := cmd.Flags().GetString("user-id")
 
-		if (email == "") == (userID == "") {
-			return fmt.Errorf("exactly one of --email or --user-id is required")
-		}
-
 		cfg, err := loadConfig()
 		if err != nil {
 			return err
@@ -221,10 +217,6 @@ var contactsUpdateCmd = &cobra.Command{
 		email, _ := cmd.Flags().GetString("email")
 		userID, _ := cmd.Flags().GetString("user-id")
 
-		if email == "" && userID == "" {
-			return fmt.Errorf("at least one of --email or --user-id is required")
-		}
-
 		cfg, err := loadConfig()
 		if err != nil {
 			return err
@@ -269,10 +261,6 @@ var contactsDeleteCmd = &cobra.Command{
 		email, _ := cmd.Flags().GetString("email")
 		userID, _ := cmd.Flags().GetString("user-id")
 
-		if (email == "") == (userID == "") {
-			return fmt.Errorf("exactly one of --email or --user-id is required")
-		}
-
 		cfg, err := loadConfig()
 		if err != nil {
 			return err
@@ -323,6 +311,8 @@ func formatCustomValue(v any) string {
 func init() {
 	contactsFindCmd.Flags().StringP("email", "e", "", "Contact email address")
 	contactsFindCmd.Flags().StringP("user-id", "u", "", "Contact user ID")
+	contactsFindCmd.MarkFlagsOneRequired("email", "user-id")
+	contactsFindCmd.MarkFlagsMutuallyExclusive("email", "user-id")
 	contactsCmd.AddCommand(contactsFindCmd)
 
 	contactsCreateCmd.Flags().StringP("email", "e", "", "Contact email address")
@@ -335,10 +325,13 @@ func init() {
 	contactsUpdateCmd.Flags().StringP("email", "e", "", "Contact email address")
 	contactsUpdateCmd.Flags().StringP("user-id", "u", "", "User ID")
 	addContactFieldFlags(contactsUpdateCmd)
+	contactsUpdateCmd.MarkFlagsOneRequired("email", "user-id")
 	contactsCmd.AddCommand(contactsUpdateCmd)
 
 	contactsDeleteCmd.Flags().StringP("email", "e", "", "Contact email address")
 	contactsDeleteCmd.Flags().StringP("user-id", "u", "", "Contact user ID")
+	contactsDeleteCmd.MarkFlagsOneRequired("email", "user-id")
+	contactsDeleteCmd.MarkFlagsMutuallyExclusive("email", "user-id")
 	contactsCmd.AddCommand(contactsDeleteCmd)
 
 	rootCmd.AddCommand(contactsCmd)
diff --git a/cmd/contacts_suppression.go b/cmd/contacts_suppression.go
index ba8046a..9d9230f 100644
--- a/cmd/contacts_suppression.go
+++ b/cmd/contacts_suppression.go
@@ -26,10 +26,6 @@ var contactsSuppressionCheckCmd = &cobra.Command{
 		email, _ := cmd.Flags().GetString("email")
 		userID, _ := cmd.Flags().GetString("user-id")
 
-		if (email == "") == (userID == "") {
-			return fmt.Errorf("exactly one of --email or --user-id is required")
-		}
-
 		cfg, err := loadConfig()
 		if err != nil {
 			return err
@@ -68,10 +64,6 @@ var contactsSuppressionRemoveCmd = &cobra.Command{
 		email, _ := cmd.Flags().GetString("email")
 		userID, _ := cmd.Flags().GetString("user-id")
 
-		if (email == "") == (userID == "") {
-			return fmt.Errorf("exactly one of --email or --user-id is required")
-		}
-
 		cfg, err := loadConfig()
 		if err != nil {
 			return err
@@ -95,10 +87,14 @@ var contactsSuppressionRemoveCmd = &cobra.Command{
 func init() {
 	contactsSuppressionCheckCmd.Flags().StringP("email", "e", "", "Contact email address")
 	contactsSuppressionCheckCmd.Flags().StringP("user-id", "u", "", "Contact user ID")
+	contactsSuppressionCheckCmd.MarkFlagsOneRequired("email", "user-id")
+	contactsSuppressionCheckCmd.MarkFlagsMutuallyExclusive("email", "user-id")
 	contactsSuppressionCmd.AddCommand(contactsSuppressionCheckCmd)
 
 	contactsSuppressionRemoveCmd.Flags().StringP("email", "e", "", "Contact email address")
 	contactsSuppressionRemoveCmd.Flags().StringP("user-id", "u", "", "Contact user ID")
+	contactsSuppressionRemoveCmd.MarkFlagsOneRequired("email", "user-id")
+	contactsSuppressionRemoveCmd.MarkFlagsMutuallyExclusive("email", "user-id")
 	contactsSuppressionCmd.AddCommand(contactsSuppressionRemoveCmd)
 
 	contactsCmd.AddCommand(contactsSuppressionCmd)
diff --git a/cmd/events.go b/cmd/events.go
index 2c71ed0..a62d4ab 100644
--- a/cmd/events.go
+++ b/cmd/events.go
@@ -58,9 +58,6 @@ func eventsSendRunE(cmd *cobra.Command, args []string) error {
 
 	email, _ := cmd.Flags().GetString("email")
 	userID, _ := cmd.Flags().GetString("user-id")
-	if email == "" && userID == "" {
-		return fmt.Errorf("at least one of --email or --user-id is required")
-	}
 
 	eventName := args[0]
 	idempotencyKey, _ := cmd.Flags().GetString("idempotency-key")
@@ -123,6 +120,7 @@ func addEventsSendFlags(cmd *cobra.Command) {
 
 func init() {
 	addEventsSendFlags(eventsSendCmd)
+	eventsSendCmd.MarkFlagsOneRequired("email", "user-id")
 	eventsCmd.AddCommand(eventsSendCmd)
 	rootCmd.AddCommand(eventsCmd)
 }