Manual:$wgShowExceptionDetails

Debug: $wgShowExceptionDetails
If set to true, uncaught exceptions will print a detailed stack trace to output.
Introduced in version:	1.8.1 (r16944)
Removed in version:	Still in use
Allowed values:	(boolean)
Default value:	false
Other settings: Alphabetical | By function

Details

If set to true, uncaught exceptions will print a detailed stack trace to output, with argument values replaced with type names. This should only be used for debugging, as it may reveal private information in function parameters due to PHP's backtrace formatting.

With the default false, users are shown only an error message "Fatal exception of type "MWException"" with an alphanumeric code that a person with access to the server logs can use to find the stack trace. Without this information, it's impossible to help fix the error.

To enable this, add the following line to your LocalSettings.php :

$wgShowExceptionDetails = true;