Developers of Moodle code have some special tools included in the Moodle package to assist them. Most of the tools should ONLY be used on test sites (not production sites). However there are a couple which may be used by a cautious administrator.
Settings > Site administration > Development > Debugging
At certain times a site administrator will need to see more and/or a more complete error message. The default is to show NONE. These messages can also 1) be very confusing to teachers and students when they suddenly appear and 2) can reveal things about your Moodle and web server that should not be common knowledge. Thus use with care and for short periods of time. See Debugging for details.
Purge all caches
Settings > Site administration > Development > Purge all caches
Moodle can cache themes, language strings, filters and other bits of information that have been calculated and stored by the web browser. This link forces all user web browsers to refresh their screens of any information that Moodle has cached. Several modules that use cache have settings which will turn off caching for that module. Eliminating or purging caches slows performance.
Moodle includes a few experimental features which a cautious administrator may consider enabling. See Experimental settings for details.