About URI scheme

about is an internal URI scheme also known as a "URL scheme" implemented in various web browsers to reveal internal state and built-in functions. It is an IANA officially registered scheme, and is standardized.
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.
In early versions of Netscape, any URI beginning with 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 data: URI scheme 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!".

Standardization

In 2010, and onwards, there are efforts to standardize the about 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

Chrome and Chromium derivatives

The following applies to all web browsers that derive from the Chromium project, including Google Chrome, Microsoft Edge, Opera, and Vivaldi.

URI	Purpose
about:cache	Deprecated in version 66
about:crash	Crashes the current rendering process.
about:credits	Displays the list of free and open source software used in the browser, and their associated licenses.
about:dino	Displayed when the browser cannot connect to the target URL, this page contains an Easter Egg: Pressing the Space Bar key starts the _Dino_ minigame, which involves making a dinosaur jump over obstacles. Microsoft Edge doesn't feature this page, having replaced it with `about:surf`
about:dns	Displays the DNS records
about:flags	Displays a page where experimental features can be configured by setting feature flags.
about:gpu	Displays information about WebGL and hardware accelerated graphics.
about:histograms	Displays histograms
about:inducebrowsercrashforrealz	Crashes the Google Chrome browser. This is designed for developers to test what happens when the Google Chrome browser crashes. Additionally, crashes Chromebooks entirely due to them running on Google Chrome.
about:internets	On particular versions of Windows, displays a page entitled "Don't Clog the Tubes!" which renders a page with an animation of the Microsoft Windows "3D Pipes" screensaver. Does not work on Windows Vista due to the pipes screen saver no longer being supported for releases after the 2.0.169.1 release.
about:kill	Same as about:crash, but with a violet background color and the message "He's Dead, Jim!" Occurs when the OS runs out of memory or the browser is killed by an external cause, such as the OS shutting down.
about:labs	Moved to about:flags in Chrome Dev channel 8.0.552.11
about:memory	Displays the process manager
about:net-internals	Provides an interface for monitoring the network usage and performance statistics
about:plugins	Shows installed plug-ins
about:sandbox	Shows which sandbox protection mechanisms are currently enabled.
about:shorthang	Hangs the tab's process, making it become unresponsive. This is designed for testing the hanging protection.
about:stats	Displays statistics about processes. At the top of the page, it states "Shhh! This page is secret!"
about:version	Displays version information, same as about:

The above list is not exhaustive; for a full list, see about:about URI.

Firefox

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 (v1–15)

In Opera, about: is an alias for the opera: scheme; therefore all these URIs also work with about prefixed. User JavaScript is disabled for all URIs in the about: or opera: schemes as a security feature. These pages can, however, be styled using local stylesheets.
Despite using an Opera derivative, the Nintendo DS Browser does not support any of the following functions; the Nintendo DSi Browser, however, does support opera:about.

URIs	Purpose
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 the browser's Web Storage
opera:webdatabases	Shows the browser's Web Storage databases
opera:gpu	Shows information about hardware accelerated graphics and GPU support
opera:cpu	Displays CPU usage

Internet Explorer (6–11)

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.
Any about URI that is not recognized by Internet Explorer redirects to a page saying "Navigation to the webpage was canceled."

URI	Purpose	Supported versions
about:home	Displays the user's home page.	6, 7, 9, 10, 11
about:desktopitemnavigationfailure	Displays the "navigation cancelled" page.	6–8
about:navigationcanceled	Displays the "navigation cancelled" page.	6–8
about:navigationfailure	Displays the "navigation cancelled" page.	6–8
about:noadd-ons	Appears when add-ons are disabled to notify the users of a change in their web browsing experience.	7–11
about:noadd-onsinfo	Contains information about add-ons and what they do.	7–11
about:offlineinformation	Informs the user that the current page cannot be viewed offline. Internet Explorer 9 and later do not support offline browsing.	6–8
about:postnotcached	Informs the user that the current page needs to refresh and any information entered in a form will have to be re-posted.	6–11
about:securityrisk	Informs the user not to browse with the current security settings because they may be harmful to the computer.	6–11
about:tabs	Informs the user about tabbed browsing. Internet Explorer shows this page upon creating a new tab if the "Open home page for new tabs instead of a blank page" setting is enabled.	7–11
about:inprivate	Appears when the use initiates InPrivate Browsing; contains information about this feature.	9–11
about:compat	Displays a table of sites and the document rendering emulation mode configured for maximum backward compatibility.	11
about:newsfeed	Displays Internet Explorer 11's signature start page. It contains a Microsoft Bing search bar at the top, followed by a customizable row of tiles pertaining bookmarked website, a row of news topic category selection links, and an infinitely scrolling news aggregation feed.	11