According to this question, it's possible to turn on/off WP_DEBUG for specific sites on a multisite.

Is it possible to do this with a sub-directory multisite?

2 Answers 2


You can do this by adding some code to wp-config.php

$request_uri = $_SERVER['REQUEST_URI'];
$debug_dirs = array ('/debug-dir1/','/debug-dir2/'); // list of directories to turn on debugging
foreach ($debug_dirs as $debug_dir) {
    if (!strncmp($request_uri,$debug_dir,strlen($debug_dir))) {
        define('WP_DEBUG', true);
define('WP_DEBUG', false); // debug off by default
  • doesn't work for me (WP 3.8.1). maybe it's because the debug_dirs only exist virtually through permalinks and aren't actual folders!? Commented Jan 30, 2014 at 22:48
  • Sorry, I had it working and then changed it when I pasted the code in here. The problem is that defining WP_DEBUG should only happen once. The default WP_DEBUG setting (false) has to happen at the very end and not the beginning!
    – user42826
    Commented Jan 30, 2014 at 23:53

Here is what worked for me

$url = 'http://' . $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'];
if (strpos($url,'sitename') !== false) {
            define('WP_DEBUG', true);

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