apply_filters( 'query_vars', string[] $public_query_vars )

More Information

This filter allows query vars to be added, removed, or changed prior to executing the query.

Example

function myplugin_query_vars( $qvars ) {
	$qvars[] = 'custom_query_var';
	return $qvars;
}
add_filter( 'query_vars', 'myplugin_query_vars' );