wp_nav_menu_items

When it fires

WordPress applies wp_nav_menu_items inside wp_nav_menu(), after it has built the items for a menu and before it wraps them in the . You get the items as one HTML string, plus the arguments the theme passed.

It only works with classic menus. Block themes use the Navigation block, which doesn't call wp_nav_menu().

Parameters

Parameters

$itemsstring	The HTML list content for the menu items.
$argsstdClass	An object containing wp_nav_menu() arguments.

What to return

The menu items as an HTML string.

Example: Add a Log in / Log out link to the main menu

add_filter( 'wp_nav_menu_items', function ( $items, $args ) {
	if ( 'primary' !== $args->theme_location ) {
		return $items;
	}
	if ( is_user_logged_in() ) {
		$url   = wp_logout_url( home_url( '/' ) );
		$label = __( 'Log out', 'my-snippets' );
	} else {
		$url   = wp_login_url();
		$label = __( 'Log in', 'my-snippets' );
	}
	$items .= sprintf(
		'<li class="menu-item menu-item-login"><a href="%1$s">%2$s</a></li>',
		esc_url( $url ),
		esc_html( $label )
	);
	return $items;
}, 10, 2 );

Good to know

• Check $args->theme_location so you only change the menu you mean. Location names vary by theme; look for register_nav_menus() in the theme's code.
• To target one menu by its slug, use the wp_nav_menu_{$menu->slug}_items filter.
• If no menu is assigned to the location, the theme's fallback is shown and this filter doesn't run.