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Developer(s) Apple, KDE, Nokia, Google, RIM, Palm, others.
Preview release neutral builds
Written in C++
Operating system Cross-platform
Type Layout engine
License GNU LGPL - components
BSD-style license - rest

WebKit is a layout engine designed to allow web browsers to render web pages. The WebKit engine provides a set of classes to display web content in windows, and implements browser features such as following links when clicked by the user, managing a back-forward list, and managing a history of pages recently visited.

WebKit was originally created as a fork of KHTML as the layout engine for Apple's Safari; it is portable to many other computing platforms.

WebKit's WebCore and JavaScriptCore components are available under the GNU Lesser General Public License, and the rest of WebKit is available under a BSD-style license.[1]



WebKit was originally derived by Apple Inc. from the Konqueror browser’s KHTML software library for use as the engine of Mac OS X’s Safari web browser and has now been further developed by individuals from the KDE project, Apple Inc., Nokia, Google, Bitstream, Torch Mobile and others.[2]



The code that would become WebKit began in 1998 as the KDE project’s HTML layout engine KHTML and KDE's JavaScript engine (KJS). The name and project 'WebKit' were created in 2002 when Apple Inc. created a fork of KHTML and KJS. Apple developers explained in an e-mail to KDE developers[3] that these engines allowed easier development than other technologies by virtue of being small (less than 140,000 lines of code), cleanly designed and standards compliant. KHTML and KJS were ported to Mac OS X with the help of an adapter library and renamed WebCore and JavaScriptCore.[3] JavaScriptCore was announced in an e-mail to a KDE mailing list in June 2002, alongside the first release of Apple's changes.[4] WebCore was announced at the Macworld Expo in January 2003 by Apple CEO Steve Jobs with the release of the Safari web browser. JavaScriptCore was first included with Mac OS X v10.2 as a private framework which Apple used within their Sherlock application, while WebCore debuted with the first beta of Safari. Mac OS X v10.3 was the first major release of Apple's operating system to bundle WebKit, although it had already been bundled with a minor release of 10.2.

However, the exchange of code patches between the two branches of KHTML has previously been difficult and the code base diverged because both projects had different approaches in coding.[5] One of the reasons for this is that Apple worked on their version of KHTML for a year before making their fork public.

Despite this, the KDE project was able to incorporate some of these changes to improve KHTML's rendering speed and add features, including compliance with the Acid2 rendering test.[citation needed] Konqueror 3.5 passed the Acid2 test, which was released after Apple had opened its WebKit CVS and Bug Database.

According to Apple, some changes involved Mac OS X-specific features (e.g., Objective-C, KWQ, Mac OS X calls) that are absent in KDE's KHTML, which called for different development tactics.[6]

Split development

At one point KHTML developers said they were unlikely to accept Apple's changes and claimed the relationship between the two groups was a "bitter failure".[7] Apple submitted their changes in large patches that contained a great number of changes with inadequate documentation, often to do with future feature additions. Thus, these patches were difficult for the KDE developers to integrate back into KHTML. Furthermore, Apple had demanded developers to sign nondisclosure agreements before looking at Apple's source code and even then they were unable to access Apple's bug database.[8]

During the publicized 'divorce' period, KDE developer Kurt Pfeifle (pipitas) posted an article claiming KHTML developers had managed to backport many (but not all) Safari improvements from WebCore to KHTML, and they always appreciated the improvements coming from Apple and still do so. The article also noted Apple had begun to contact KHTML developers about discussing how to improve the mutual relationship and ways of future cooperation.[9]

Since the story of the fork appeared in news, Apple has released changes of the source code of its KHTML fork in a CVS repository.[10] Since the transfer of the sourcecode into a public CVS repository, Apple and KHTML developers have had increasing collaboration. Many KHTML developers have become reviewers and submitters for Apple's WebKit SVN repository.

The WebKit team had also reversed many Apple-specific changes in the original WebKit code base and implemented platform-specific abstraction layers to make committing the core rendering code to other platforms significantly easier.[11]


On June 7, 2005, Safari developer Dave Hyatt announced on his weblog that Apple was open-sourcing WebKit (previously, only WebCore and JavaScriptCore were open source) and opening up access to WebKit’s CVS tree and Bugzilla tool.[10] This was announced at Apple’s Worldwide Developers Conference 2005 by Apple Senior Vice President of Software Engineering Bertrand Serlet.

In mid-December 2005 support for Scalable Vector Graphics was merged into the standard build[12] and in early January 2006 the source code was migrated from CVS to Subversion. In July 2007, the Ars Technica website published an article reporting that the KDE team would move from KHTML to WebKit.[13] This move is still in discussion in the KDE community and no official information confirmed it.

WebKit's JavaScriptCore and WebCore components are available under the GNU Lesser General Public License, while the rest of WebKit is available under a BSD-style license.

Further development

In November 2007, the project announced that it had accomplished support for HTML 5 media features, allowing for embedded video to be natively rendered and script-controlled in WebKit.[14]

On June 2, 2008, the WebKit project announced they rewrote JavaScriptCore as "SquirrelFish", a bytecode interpreter.[15][16] The project evolved into SquirrelFish Extreme (abbreviated SFX), announced on September 18, 2008, which compiles JavaScript into native machine code, eliminating the need for a bytecode interpreter and thus speeding up Javascript execution.[17] Initially the only supported architecture for SFX was the x86 architecture, but at the end of January 2009 SFX was enabled for Mac OS X on x86-64 architectures as it passes all tests on that platform.[18]

Beginning in early 2007, the development team began to implement CSS extensions, including animation, transitions and both 2D and 3D transforms;[19] such extensions were released as working drafts to the W3C in 2009 for standardization.[20]


WebKit is used as the rendering engine within Safari on Windows, Mac OS X and iPhone OS. Other applications on Mac OS X can make use of WebKit, for example Apple's e-mail client Mail and the 2008 version of Microsoft's Entourage personal information manager both make use of WebKit to render e-mail messages with HTML content, as does the Claws Mail e-mail client via the Fancy Plugin.

New web browsers have been built around WebKit such as the S60 browser[21] on Symbian mobile phones, Midori, Shiira, Google's Chrome browser,[22][23] and Uzbl, also it has been adopted as the rendering engine in OmniWeb, iCab and Epiphany replacing their original rendering engines.[24] Epiphany supported both Gecko and WebKit for some time, but the team decided that Gecko's release cycle and future development plans would make it cumbersome to continue supporting it. Palm's WebOS is also based on WebKit. The latest interface update for Valve Corporation's Steam uses WebKit for rendering of its interface and built in browser.[25]


The week after Hyatt's announcement of WebKit's open-sourcing, Nokia announced that it had ported WebKit to the Symbian operating system and was developing a browser based on WebKit for mobile phones running S60. Now named Web Browser for S60, it is used on Nokia, Samsung, LG, and other Symbian S60 mobile phones. Apple has also ported WebKit to the iPhone OS to run on the iPhone and iPod Touch, where it is used to render content within the device’s web browser and e-mail software,[26] the Android mobile phone platform uses WebKit as the basis of its web browser,[27] and the Palm Pre, announced January 2009, has an interface based on WebKit.[28]

In June 2007, Apple announced that WebKit had been ported to Microsoft Windows as part of Safari. There are also ongoing ports for the open source operating systems Syllable,[29] Haiku[30] and AROS.[31]

WebKit has also been ported to a number of toolkits that support multiple platforms, such as the GTK+ toolkit,[32] the Qt toolkit[33] and the Adobe Integrated Runtime. Qt Software includes the Qt port in the Qt 4.4 release. The Qt port of WebKit is also available to be used in Konqueror in KDE 4.1.[13] The Iris Browser on Qt also uses WebKit.

There is also a project synchronized with WebKit (sponsored by Pleyo)[34] called Origyn Web Browser, which provides a meta-port to an abstract platform with the aim of making porting to embedded or lightweight systems quicker and easier.[35] This port is used for embedded devices such as set-top boxes, PMP and it has been ported also into AmigaOS 4.1, AmigaOS 3.9 for Classic Amiga machines, AROS[36][37][38] and MorphOS. MorphOS version 1.7 it it the first version of OWB sporting HTML5 media tags.[39][40]



WebCore is a layout, rendering, and Document Object Model (DOM) library for HTML and SVG, developed by the WebKit project. Its complete source code is licensed under the LGPL. The WebKit framework wraps WebCore and JavaScriptCore, providing an Objective-C application programming interface to the C++-based WebCore rendering engine and JavaScriptCore script engine, allowing it to be easily referenced by applications based on the Cocoa API; later versions also include a cross-platform C++ platform abstraction, and various ports provide additional APIs.

WebKit passes the Acid2 and Acid3 tests, with pixel-perfect rendering and no timing or smoothness issues on reference hardware.[41]


JavaScriptCore is a framework that provides a JavaScript engine for WebKit implementations, and provides this type of scripting in other contexts within Mac OS X.[42][4] JavaScriptCore is originally derived from KDE's JavaScript engine (KJS) library (which is part of the KDE project) and the PCRE regular expression library. Since forking from KJS and PCRE, JavaScriptCore has been improved with many new features and greatly improved performance.[43]

On June 2, 2008, the WebKit project announced they rewrote JavaScriptCore as "SquirrelFish", a bytecode interpreter.[15][16] The project evolved into SquirrelFish Extreme (abbreviated SFX, marketed as Nitro), announced on September 18, 2008, which compiles JavaScript into native machine code, eliminating the need for a bytecode interpreter and thus speeding up JavaScript execution.[17]


Drosera is a JavaScript debugger that was included with the nightly builds of WebKit.[44][45] It was named after Drosera, a genus of carnivorous plants (i.e. bug-eaters). Drosera has been replaced by the inclusion of debugging functionality in the Web Inspector.[46]


A benchmark suite that aims to measure JavaScript performance on tasks that are relevant to the current and near future use of JavaScript in the real world, such as encryption and text manipulation.[47] The suite further attempts to be balanced and statistically sound.[48] It was released by Apple's WebKit team in December 2007.[49] It was well-received,[50] and other browser developers also use it to compare the JavaScript performance of different browsers.[51]

See also


  1. ^ "Open Source - WebKit". Apple. Retrieved 2009-03-05. 
  2. ^ Maciej Stachowiak (November 9, 2008). "Companies and Organizations that have contributed to WebKit". WebKit Wiki. Retrieved 2008-11-17. 
  3. ^ a b KDE KFM-Devel mailing list "(fwd) Greetings from the Safari team at Apple Computer", January 7, 2003.
  4. ^ a b Stachowiak, Maciej (June 13, 2002). "JavaScriptCore, Apple's JavaScript framework based on KJS". kde-darwin mailing list. Retrieved 2008-08-21. 
  5. ^ "So, when will KHTML merge all the WebCore changes?". Retrieved 2010-02-20. 
  6. ^ "Safari and KHTML again". 2005-04-30. Retrieved 2010-02-20. 
  7. ^ The bitter failure named "safari and khtml"
  8. ^ Open-source divorce for Apple's Safari?
  9. ^ WebCore - KHTML - Firefox: Know your facts!
  10. ^ a b Daniel Molkentin (June 7, 2005). "Apple Opens WebKit CVS and Bug Database". KDE News. Retrieved 2007-01-16. 
  11. ^ Ars at WWDC: Interview with Lars Knoll, creator of KHTML
  12. ^ Next Generation KDE Technologies Ported to WebCore
  13. ^ a b Unrau, Troy (2007-07-23). "The unforking of KDE’s KHTML and WebKit". Ars Technica. Retrieved 2007-07-30. 
  14. ^ HTML5 Media Support by Antti Koivisto, Surfin' Safari blog, November 12th, 2007
  15. ^ a b Announcing SquirrelFish
  16. ^ a b SquirrelFish project
  17. ^ a b Introducing SquirrelFish Extreme
  18. ^
  19. ^ CSS Transforms
  20. ^ CSS3 Animations
  21. ^ Nokia S60 Webkit Browser
  22. ^ Google Chrome, Google’s Browser Project
  23. ^ Comic describing the Google Chrome Project
  24. ^ Epiphany Mailing list - ANNOUNCEMENT: The Future of Epiphany
  25. ^ A Brand New Steam
  26. ^ Maciej Stachowiak (January 10, 2007). "The Obligatory iPhone Post". Surfin' Safari weblog. Retrieved 2008-01-24. 
  27. ^ Android Uses WebKit
  28. ^ Palm Pre in-depth impressions, video, and huge hands-on gallery
  29. ^ Syllable WebKit Port, Syllable Server
  30. ^ Webkit port: talking to Andrea "xeD" Anzani | Haiku Project
  31. ^ Cow launched! | Robert Norris´ Blog on porting WebKit to AROS
  32. ^ Alp Toker – WebKit/Gtk+ is coming
  33. ^ QT WebKit
  34. ^ pleyo
  35. ^ See OWB forge
  36. ^ AmigaOS OWB official page
  37. ^ [1]
  38. ^ AROS OWB developer page
  39. ^ "Origyn Web Browser for MorphOS". Fabian Coeurjoly. 
  40. ^ Thom Holwerda (March 8, 2010). "Origyn Web Browser 1.7 Supports HTML5 Media, More". OSNews. 
  41. ^ Maciej Stachowiak (2008-09-25). "Full Pass Of Acid3". Surfin' Safari - The WebKit Blog. Retrieved 2008-09-29. 
  42. ^ The WebKit Open Source Project – JavaScript
  43. ^ "The Great Browser JavaScript Showdown". 2007-12-19. 
  44. ^ Drosera wiki article
  45. ^ "Introducing Drosera". Surfin’ Safari. 
  46. ^ "Commit removing Drosera". 
  47. ^ Muchmore, Michael (2008-06-18). "Review: Firefox 3 Stays Ahead of Browser Pack".,2933,368182,00.html. Retrieved 2008-09-06. 
  48. ^ "SunSpider JavaScript Benchmark". Retrieved 2008-09-06. 
  49. ^ "Announcing SunSpider 0.9". 2007-12-18. Retrieved 2008-09-06. 
  50. ^ Atwood, Jeff (2007-12-19). "The Great Browser JavaScript Showdown". Retrieved 2008-09-06. 
  51. ^ Resig, John (2008-09-03). "JavaScript Performance Rundown". Retrieved 2008-06-09. 

External links

Simple English

WebKit is a layout engine made to let web browsers show web pages. The WebKit engine has a set of classes to display web content in windows, and implements browser features such as following links when clicked by the person using the web browser (the user), managing a back-forward list, and keeping a history of pages recently visited. WebKit was first made to be used as the layout engine for Safari, and is portable to many other computing platforms. WebKit's WebCore and JavaScriptCore parts are available under the GNU Lesser General Public License, and the rest of WebKit is available under a BSD-style license.


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