Simple seo-friendly custom $_GET url rewrite with htaccess

First, add a WordPress page named game to direct requests to.

Next, add the game query var so WordPress knows what it is:

add_filter( 'query_vars', 'wpa_query_vars' );
function wpa_query_vars( $query_vars ){
    $query_vars[] = 'game';
    return $query_vars;
}

Then, add a rewrite rule to handle the incoming requests and direct them to your page:

add_action( 'init', 'wpa_add_game_rule' );  
function wpa_add_game_rule() {   
    add_rewrite_rule(  
        'game/([^/]+)/?',
        'index.php?pagename=game&game=$matches[1]',
        'top'
    );   
}

Last, create a template named page-game.php and add get_query_var( 'game' ) to see the requested game.

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