'AutoAuthenticate': called to authenticate users on external/environmental means
$user: writes user object to this parameter
+'BadImage': When checking against the bad image list
+$name: Image name being checked
+&$bad: Whether or not the image is "bad"
+
+Change $bad and return false to override. If an image is "bad", it is not
+rendered inline in wiki pages or galleries in category pages.
+
'BlockIp': before an IP address or user is blocked
$block: the Block object about to be saved
$user: the user _doing_ the block (not the one being blocked)
$oldRev: Revision object of the "old" revision (may be null/invalid)
$newRev: Revision object of the "new" revision
+'EditFormPreloadText': Allows population of the edit form when creating new pages
+&$text: Text to preload with
+&$title: Title object representing the page being created
+
'EditFilter': Perform checks on an edit
$editor: Edit form (see includes/EditPage.php)
$text: Contents of the edit box
$subject: subject of the mail
$text: text of the mail
+'FetchChangesList': When fetching the ChangesList derivative for a particular user
+&$user: User the list is being fetched for
+&$skin: Skin object to be used with the list
+&$list: List object (defaults to NULL, change it to an object instance and return
+false override the list derivative used)
+
'GetInternalURL': modify fully-qualified URLs used for squid cache purging
$title: Title object of page
$url: string value as output (out parameter, can modify)
$wcOnlySysopsCanPatrol: config setting indicating whether the user
must be a sysop to patrol the edit
+'MathAfterTexvc': after texvc is executed when rendering mathematics
+$mathRenderer: instance of MathRenderer
+$errmsg: error message, in HTML (string). Nonempty indicates failure
+ of rendering the formula
+
'OutputPageBeforeHTML': a page has been processed by the parser and
the resulting HTML is about to be displayed.
$parserOutput: the parserOutput (object) that corresponds to the page
&$personal_urls: Array of link specifiers (see SkinTemplate.php)
&$title: Title object representing the current page
+'SiteNoticeBefore': Before the sitenotice/anonnotice is composed
+&$siteNotice: HTML returned as the sitenotice
+Return true to allow the normal method of notice selection/rendering to work,
+or change the value of $siteNotice and return false to alter it.
+
+'SiteNoticeAfter': After the sitenotice/anonnotice is composed
+&$siteNotice: HTML sitenotice
+Alter the contents of $siteNotice to add to/alter the sitenotice/anonnotice.
+
'TitleMoveComplete': after moving an article (title)
$old: old title
$nt: new title
to use this hook.
$content_actions: The array of content actions
+'BeforePageDisplay': Called just before outputting a page (all kinds of,
+ articles, special, history, preview, diff, edit, ...)
+ Can be used to set custom CSS/JS
+$out: OutputPage object
More hooks might be available but undocumented, you can execute
./maintenance/findhooks.php to find hidden one.