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about is an internalURI scheme also known as a "URL scheme" (or, erroneously, "protocol") implemented in variousweb browsers to reveal internal state and built-in functions. It is an IANAofficially registered scheme, and is standardized.[1]
The most commonly implementedabout URIs areabout:blank, which displays a blankHTML document, and simplyabout:, which may display information about the browser. Some browsers use URIs beginning with the name of the browser for similar purposes, and manyabout URIs will be translated into the appropriate URI if entered. Examples areopera (Opera) orchrome (Google Chrome). An exception isabout:blank, which is not translated.
In early versions ofNetscape, anyURI beginning withabout: that wasn't recognized as a built-in command would simply result in the text after the colon being displayed. Similarly, in early versions ofInternet Explorer,about: followed by a string ofHTML (e.g.about:<em>hello world</em>) would render that string as though it were the source of the page — thus providing a similar (though more limited) facility to thedata: URI scheme defined byRFC 2397. Still other versions of Netscape would return various phrases in response to an unknownabout URI, including "Whatchew talkin' 'bout, Willis?" (a catch phrase from the TV showDiff'rent Strokes) or "Homey don't play dat!" (from a recurringskit on the TV showIn Living Color).[2][3]
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 (APPSAWG).[4] In August 2012, it was published as an officialRequest for Comments asRFC 6694. Theabout URIs that have since been defined and assigned byIANA are listed below.[5]
| URI | Purpose |
|---|---|
| about:blank[6] | 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 withinHTML5 intended for use in theDOCTYPE designed for compatibility with some legacy authoring tools, such asXSLT, 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 withinHTML5 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.[7] |
| about:html-kind | Used as an identifier for kinds of media tracks.[8] |
| URI | Purpose | |||||
|---|---|---|---|---|---|---|
| Firefox,SeaMonkey,Mozilla | Google Chrome,Chromium | Konqueror | Opera | Edge | Internet Explorer | |
| about: | Deprecated inFirefox 57 (Firefox Quantum) | Redirects to "chrome://version" | Redirects to "about:konqueror" | Redirects to "opera:about" | Redirects to "edge://version" | — |
| about:about | Lists all the about: URLs (Firefox since version 4.0) | Redirects to "chrome://about"; Lists all the chrome: URIs (Works like "chrome://chrome-urls") | Redirects to "about:konqueror" | Redirects to "opera:about" | Redirects to "edge://edge-urls" | — |
| about:blank | Shows a blank document | |||||
| about:plugins | Shows the filename,MIME type, description, suffix, and status of all installed plug-ins | Deprecated in Chrome 57[9] | Shows the filename,MIME type, description, suffix, and status of all installed plug-ins | Redirects to "opera:plugins" | — | — |
| about:cache | Shows information about the Cache Service. | Deprecated in Chrome 66[10] | Redirects to "about:konqueror" | Redirects to "opera:cache" | — | — |
| about:mozilla | Shows a page from the fictionalBook of Mozilla. In some versions of Netscape, also replaced the meteors in the standard Netscapethrobber with a large fire-breathing lizard. | — | Redirects to "about:konqueror" | — | — | Shows a blank HTML document with ablue background. Removed inWindows XPSP2. (The blue page can still be seen at "res://mshtml.dll/about.moz" instead.) |
The following applies to all web browsers that derive from theChromium project, includingGoogle Chrome,Microsoft Edge,Opera, andVivaldi.
| URI[11] | Purpose |
|---|---|
| about:cache | Deprecated in version 66[10] |
| about:crash | Crashes the current rendering process. (This causes the "Aw, snap!" crash notification page to be displayed.) |
| 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 withabout:surf (see below.)[12] |
| about:dns | Displays the DNS records |
| about:flags | Displays a page where experimental features can be configured by settingfeature 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 theMicrosoft Windows "3D Pipes" screensaver. Does not work onWindows Vista due to the pipes screen saver no longer being supported for releases after the 2.0.169.1 release. |
| about:kill | Same asabout: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 toabout: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 (Deprecated in Chrome 57)[9] |
| 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 asabout: |
The above list is not exhaustive; for a full list, seeabout:about URI.
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.[13]
| URIs | Purpose | |
|---|---|---|
| Firefox | SeaMonkey,Mozilla Application Suite | |
| about:addons | Shows installed addons, plugins, themes, and provides an interface for installing new addons (Firefox 4+ and SeaMonkey 2.1+) | |
| about:app-manager | Shows theFirefox OS Simulator | — |
| about:bloat | Displays BloatView output (disabled in release builds). Superseded byabout:memory on Gecko 1.9.2.[14] | — |
| about:bloat?new | TBA | — |
| about:bloat?clear | TBA | — |
| about:blocked | Shows themalware protection page used when the browser identifies a page as not safe for viewing (Firefox 3+) | — |
| about:buildconfig | Shows the arguments and options used to compile the build in use | |
| about:cache | Shows information about the Cache Service. Number of entries, location of cache, size of cache, etc. for both memory and disk cache. | |
| about:cache?device=memory | Shows individual entries in memory | |
| about:cache?device=disk | Shows individual entries on disk | |
| about:cache?device=offline | Shows individual entries for offline viewing (Gecko 1.9+) | |
| about:cache-entry | Shows information about a cache entry. Used in about:cache links. Requires parameters. | |
| about:certerror | Shows the error page used when anSSL/TLS certificate is untrusted or otherwise invalid | |
| about:config | Shows an interface for viewing and setting a wide variety of configuration variables, many of which are not otherwise accessible through theGUI (options panels). The known earliest use of about:config dates back to Netscape 4.x, where it was not possible to edit the settings from the browser. about:config settings first became modifiable inMozilla Application Suite. On first use, about:config displays a message which tells the user that the settings might void the warranty and they can be "Harmful to the stability, security, and performance of this application." The message about voiding one's warranty is a joke, as Mozilla Firefox ships without a warranty of any kind.[15] The message has a checkbox to turn it off. | |
| about:crashes | Shows details of crashes submitted by Mozilla's crash reporter (Firefox 3+, SeaMonkey 2.0+) | |
| about:credits | Shows a list of all those who contributed to Mozilla | |
| about:devtools | Shows the welcome page used by Firefox Developer Tools | |
| about:downloads | Shows a list of downloaded files | |
| about:feeds | Shows the page used when clicking the rss feed icon in the address bar | |
| about:healthreport | Shows the Firefox Health Report | |
| about:home | Shows the Firefox 4 default home page | — |
| about:jetpack | Shows an interface for viewing and setting theJetPack extension | — |
| about:licence | The equivalent ofabout:license in the British English localizations of Firefox. (SeeAmerican and British English spelling differences). Not available since Firefox 4. | |
| about:license | Shows theMozilla Public License (and theNetscape Public License) for the piece of software (Gecko 1.8+) | |
| about:logo | Shows the logo used on theabout: screen | |
| about:memory | Shows memory usage (Firefox 3.6+) | |
| about:mozilla | Easter egg, shows a verse fromThe Book of Mozilla | |
| about:neterror | Shows the error page used when the browser could not access the requested path | |
| about:newaddon | This URI is not registered. However, when the user tries tosideload an add-on, a dialog box bearing this URI appears. asking for the user's explicit consent. | — |
| about:newtab | Shows a grid of favourite and most-visited websites (Firefox 13+) | |
| about:permissions | Shows permissions for all sites on Firefox 6.0a1 | — |
| about:plugins | Shows installed, currently enabled plug-ins | |
| about:preferences | Shows the new preferences page | |
| about:privatebrowsing | Can be used to switch to private browsing mode. It shows a message indicating that Firefox will not remember any history for the current session. Note: It does not show URI on the address bar | — |
| about:reader?url= | Opens the specified URL in Reader Mode. For example,about:reader?url=http://example.com. | — |
| about:rights | Shows licensing information | |
| about:robots | Easter egg, beginning with March 8, 2008 trunk builds. The title of a window citesthe iconic phrase ofThe Day the Earth Stood Still.[16] The page's prose citesIsaac Asimov's first law of robotics. | — |
| about:sessionrestore | Shows an interface for viewing about last session. | |
| about:startpage | In Ubuntu, shows the Ubuntu start page with the current search engine (if the "Ubuntu Firefox Modifications – ubufox" add-on is installed) | |
| about:support | Shows troubleshooting information (Firefox 3.6+, SeaMonkey 2.1+) | |
| about:sync-tabs | Shows list of tabs from other computers. Requires enabled synchronization. | |
| about:tabcrashed | Contains the text displayed when atab crashes. Added in Firefox 25. | — |
| about:webrtc | Shows an interface forWebRTC internals | |
| about:welcome | Shows the welcome page used by Firefox | |
InOpera,about: is an alias for theopera: scheme; therefore all these URIs also work with about prefixed. UserJavaScript is disabled for all URIs in theabout: oropera: schemes as a security feature. These pages can, however, be styled using localstylesheets.
Despite using an Opera derivative, theNintendo DS Browser does not support any of the following functions; theNintendo DSi Browser, however, does supportopera: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 9.0 and newer) |
| 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 9.5 and newer) |
| 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. (Note: This does not work directly, all button parameters as on CustomButtons need be specified.) |
| 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 viaOpera Dragonfly (Opera 9.5 and newer) |
| opera:memdebug | Shows debug information about memory usage (Opera 9.5 and newer) |
| opera:webstorage | Shows the browser'sWeb Storage (Opera 10.5 and newer) |
| opera:webdatabases | Shows the browser's Web Storage databases (Opera 10.5 and newer) |
| opera:gpu | Shows information about hardware accelerated graphics and GPU support |
| opera:cpu | Displays CPU usage (Opera 12 beta and newer) |
Internet Explorer about URIs are configurable inWindows. 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 (although the page can still be found at "res://mshtml.dll/about.moz"). These about URIs are sometimes used for spyware and adware, most notably inCoolWebSearch, which made about:blank display advertisements.
Anyabout 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 (not 8) |
| about:desktopitemnavigationfailure | Displays the "navigation cancelled" page. | 6–8 |
| about:navigationcanceled | ||
| about:navigationfailure | ||
| 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 abouttabbed 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 initiatesInPrivate 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.[17] | 11 |
| about:newsfeed | Displays Internet Explorer 11's signature start page. It contains aMicrosoft Bing search bar at the top, followed by a customizable row of tiles pertainingbookmarked website, a row of news topic category selection links, and an infinitely scrolling news aggregation feed. | 11 |
The following applies toMicrosoft Edge Legacy version 20 through 44. For newer Edge versions, seethe Chromium section.
| URI | Purpose |
|---|---|
| about:home | Shows the content that would be shown if the home button were pressed |
| about:flags | Displays a list of Developer Setting and Experimental features |
| about:start | Shows the customizable (default) start page. |
| about:config | Redirects to about:flags |
| about:tabs | Shows the (default) new tab page. |
| about:compat | Shows the Enterprise Mode list (if configured) |
| about:edge | Shows the Edge logo. |
| about:inprivate | Shows the inprivate information tab. |
| about:surf | A surfing game easter egg. |
WhenGNOME Web (formerly Epiphany) usedGecko as its layout engine, all Firefox-specificabout: URIs worked in it. After the adoption ofWebKit as its layout engine, only the following URIs are supported.[citation needed]
| URI | Purpose |
|---|---|
| about:plugins | Shows installed plug-ins. |
| about:memory | Shows details about memory usage. |
| about:epiphany | Displays the following message:[18]
It is a quote from Chapter 3 of Saint-Exupéry's memoirTerre des Hommes (titledWind, Sand and Stars in its English translation by Lewis Galantiere). |
| about:applications | Interface for managing theWeb Application Mode, supported since release 3.2.[19] |
| 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: |
| about:incognito | Displays information about incognito mode. Is a blank page in non-incognito mode. |
The about: URL originated in and has existed in all versions ofNetscape browsers. It was originally added as anEaster egg to display information about the development team.[20]
Older versions of theNetscape browser have anabout:people URI that was similar toabout:credits above, but it would redirect to Netscape's active employee listing. In addition,about:username, whereusername is the username of a Netscape employee, would redirect to the Netscape homepage of the employee specified. For example,about:jwz would redirect tohttp://people.netscape.com/jwz/ (not an active link).[21] Not all employee pages were accessible through this scheme. Only developers who knew which file in the source tree and the encoding scheme used to obfuscate the directory of employee about entries could add their names.[citation needed]
Many otherabout: 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 asabout:deutsch showing Mozilla in Lederhosen.[22]
Some versions of Netscape would display the browser history for theabout:global URI.[22]
about URI exceptabout:blank andabout:plugins redirects toabout:konqueror, which shows a friendly ‘start’ and navigation page.about:blank.outlook:today URI, which shows the Outlook Today Screen. This screen shows messages, tasks and appointments; it is also accessible from Internet Explorer. Outlook recognizesabout:blank too, but no other "about:" URIs.