About URI scheme
about is an internal URI scheme implemented in various Web browsers to reveal internal state and built-in functions. It is an IANA officially registered scheme, and is standardized.
In early versions of Netscape, any URI beginning
about: that wasn't recognized as a built-in command would simply result in the text after the colon being displayed. Similarly, in early versions of Internet Explorer, about: followed by a string of HTML would render that string as though it were the source of the page — thus providing a similar facility to the defined by. Still other versions of Netscape would return various phrases in response to an unknown about URI, including "Whatchew talkin' 'bout, Willis?" or "Homey don't play dat!".The most commonly implemented
about URIs are about:blank, which displays a blank HTML document, and simply about:, which may display information about the browser. Some browsers use URIs beginning with the name of the browser for similar purposes, and many about URIs will be translated into the appropriate URI if entered. Examples are opera or chrome. An exception is about:blank, which is not translated.Standardization
In 2010, and onwards, there are efforts to standardize theabout URI scheme, and define the processing requirements for some specific URIs, in the IETF Applications Area Working Group. In August 2012, it was published as an official Request for Comments as. The about URIs that have since been defined and assigned by IANA are listed below.| URI | Purpose |
| about:blank | References a blank HTML document with the media type text/html and character encoding UTF-8. This is widely used to load blank pages into browsing contexts, such as iframes within HTML, which may then be modified by scripts. |
| about:legacy-compat | A reserved, though unresolvable, URI defined within HTML5 intended for use in the DOCTYPE designed for compatibility with some legacy authoring tools, such as XSLT, which may not be capable of outputting the more common, shorter alternative that lacks both the PUBLIC and SYSTEM identifiers. <!DOCTYPE html SYSTEM "about:legacy-compat">. |
| about:srcdoc | A reserved, though unresolvable, URI defined within HTML5 intended to be the URI navigated to within iframes whose content comes from the srcdoc attribute. |
| about:invalid | References a non-existent document with a generic error condition. Intended for the case where a URL is necessary, but it should not be resolveable. |
| about:html-kind | Used as an identifier for kinds of media tracks. |
Common about: URIs
Mozilla-specific about: URIs
Many of these can also be used in Thunderbird, by setting them as the "Mail Start Page". Also, some extensions define additional about: URIs not listed here.Opera (Presto)-specific about: URIs
about is an alias for opera; therefore all these URIs also work with about prefixed. User JavaScript is enabled for all URIs in the about or opera URI schemes as a security feature. These pages can, however, be styled using local stylesheets.None of these functions, except the opera:about combination, work in the Nintendo DS version of the Opera browser, the Nintendo DS Browser.
| URIs | Opera |
| opera:blank | Maps to about:blank |
| opera:about | Provides info about the browser and the configured paths. |
| about:opera | Maps to opera:about |
| opera:cache | Shows the content of the cache. |
| opera:config | Shows a page that allows changing of numerous browser preferences, many of which cannot be accessed through the normal Preferences window |
| opera:drives | Shows the local drives of the host system. |
| opera:history | Shows the content of the browser history. |
| opera:historysearch | Shows the start page of internal search engine for the browser history. |
| opera:plugins | Shows installed plug-ins. Opera 11 and newer allow individual plug-ins to be disabled from this page. |
| opera:button | Defines a custom button as a set of Opera actions. |
| opera:help | Shortcut to the help directory. This can be either local or external. |
| opera:debug | Shows a page that allows changing of settings for remote debug of Opera via Opera Dragonfly |
| opera:memdebug | Shows debug information about memory usage. |
| opera:webstorage | Shows information Web Storage. |
| opera:webdatabases | Shows information Web Storage databases. |
| opera:gpu | Shows information about hardware accelerated graphics and GPU support. |
| opera:cpu | . Displays CPU usage. |
Internet Explorer-specific about: URIs
Internet Explorer about URIs are configurable in Windows. It is therefore possible that some of the listed URIs will not work on a particular computer. For example, "about:mozilla" was removed in SP2. These about URIs are sometimes used for spyware and adware, most notably in CoolWebSearch, which made about:blank display advertisements.Note: Any
about URI that is not recognized by Internet Explorer redirects to a page saying "Navigation to the webpage was canceled"Edge-specific about: URIs
Note: Any "about:" URI is accepted, but only returns a page with the message "Well, that didn’t work".Chrome-specific about: URIs
Note: the above list is not exhaustive; for a full list, see about:about URI.Note: "about:" is usually translated to a "chrome://" URL in Chromium and newer versions of Google Chrome.
Konqueror
Note: Anyabout URI except about:blank and about:plugins redirects to about:konqueror.| URI | Konqueror |
| about:konqueror | Shows a friendly ‘start’ and navigation page |
GNOME Web
Note: When GNOME Web used Gecko as its layout engine, the andabout: URIs worked as in Mozilla Firefox. Since WebKit became Epiphany's layout engine, only these URIs are supported:| URI | GNOME Web |
| about:blank | Displays the blank page. |
| about:plugins | Shows installed plug-ins. |
| about:memory | Shows details about memory usage. |
| about:epiphany | Displays the following message: It is a quote from Chapter 3 of Saint-Exupéry's memoir Terre des Hommes. |
| about:applications | Interface for managing web applications, supported since release 3.2. |
| about:overview | Displays a grid of thumbnails for the more visited websites. |
| about:gpu | Displays information about WebGL and hardware accelerated graphics. |
| about:web | Displays the browser and its engine information, same as about: |
Netscape (historical)
The about: URL originated in and has existed in all versions of Netscape browsers. It was originally added as an Easter egg to display information about the development team.Older versions of the Netscape browser have an
about:people URI that was similar to about:credits above, but it would redirect to Netscape's active employee listing. In addition, about:username, where username is the username of a Netscape employee, would redirect to the Netscape homepage of the employee specified. For example, about:jwz would redirect to Many other about: easter eggs existed, including the famous about:mozilla, and other less known ones that showed pictures of the Netscape mascot Mozilla in various foreign garb, such as about:deutsch showing Mozilla in Lederhosen.
Some versions of Netscape would display the browser history for the
about:global URI.Internet Explorer for Mac OS 5 (historical)
In Internet Explorer for Mac 5 was an offline Easter egg, accessible by typing ‘about:tasman’, showing the Acid1 test with the text replaced by the names of the developers.Safari
Onlyabout:blank is accepted; all other about: URIs trigger default address bar behavior.Microsoft Outlook
In Microsoft Outlook, an additionaloutlook:today URI was added, which showed the Outlook Today Screen. Also, although about:blank is supported, anything else typed after about: would show that text as a web page in the browser.