// http://php.net/ob_get_level
> ob_get_level()
int(1)

http://php.net/ob_get_status
> ob_get_status()
array(5) {
  ["level"]=>
  int(1)
  ["type"]=>
  int(1)
  ["status"]=>
  int(0)
  ["name"]=>
  string(22) "default output handler"
  ["del"]=>
  bool(true)
}

According to phpinfo(), zlib.output_compression = Off and output_handler = ''. That's good. But output_buffering = 4096 (silly PHP does this by default, it has an output buffer that you can't disable but doesn't do anything, either).

When using MediaWiki (or any other PHP app that tries to do the same) to send pages gzipped, it gives up because there is an ob level already, and of a type (internal php) that it claims it can't remove.

I ran into the same issue on my localhost, solved by setting:

output_buffering = Off

in php.ini

Please apply this to tools.wmflabs.org so that we can actually send out gzipped responses (especially important for tools that get called from popular gadgets with cross-domain JSON-P requests).