This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages) This article has an unclear citation style. The references used may be made clearer with a different or consistent style of citation and footnoting. (May 2014) (Learn how and when to remove this template message) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Find sources: "Sleipnir" web browser – news · newspapers · books · scholar · JSTOR (May 2014) (Learn how and when to remove this template message) This article needs to be updated. Please help update this article to reflect recent events or newly available information. (May 2014) (Learn how and when to remove this template message)
Developer(s)Fenrir Inc, Osaka, Japan
Stable release(s) [±]
Windows (Sleipnir 6)

6.5.1 (August 2, 2023; 7 days ago (2023-08-02)[1])

Windows (Sleipnir 4)

4.8.1 (August 2, 2023; 7 days ago (2023-08-02)[2])


4.7.9 (March 2, 2021; 2 years ago (2021-03-02)[3])


4.13.2 (August 8, 2023; 1 day ago (2023-08-08)[4])

3.7.1 (January 23, 2023; 6 months ago (2023-01-23)[5])
Operating systemWindows, macOS, iOS, Android, Windows Phone
TypeWeb browser; Mobile browser
LicenseFreeware (in Japanese)

Sleipnir is a tabbed web browser developed by Fenrir Inc. The browser's main features are customization and tab functions. It supports HTML5 and multiple layout engines.

The names Sleipnir and Fenrir are both names of animals from Norse mythology.[6][7]

Sleipnir was originally created in Japanese and then released with English and Chinese translations. Further translations are performed by volunteer translators.[8][9]

It is available for iOS, macOS, Microsoft Windows, Android, and Windows Phone.


Sleipnir was originally developed by Yasuyuki Kashiwagi. In November 2004, the computer containing Sleipnir's source code was stolen.[10] In 2005, Kashiwagi established Fenrir & Co. to start development of a new version of Sleipnir. Starting with version 2, the new versions are not compatible with the original.

As of 2006 Sleipnir had 6% market share in Japan.[11]

Sleipnir was one of twelve browsers originally offered in a browser ballot screen on the EU edition of Windows 7 (and XP and Vista with an update),[12][13] so users could choose between Internet Explorer and other browsers during the installation process.

The stable version 5.0 was released on December 24, 2013 with the latest Blink engine.[14]


In the Windows version, the browser's layout engine can be changed. Internet Explorer's Trident and Mozilla's Gecko were supported. As of version, support for the WebKit rendering engine was implemented and Gecko rendering engine support was terminated.[15] Other features include tab grouping, mouse gestures, page zooming, a search bar, Greasemonkey-like user script support, and plugin support. Bookmarks on Sleipnir can be synced with different platform, using a function called Fenrir Pass.[16]

Sleipnir version 5 and onward introduce a proprietary text rendering visually resembling Mac OS text rendering. The feature is not mentioned in their Mac feature set.[original research?]


Sleipnir 2 for Windows: Sleipnir 2 features customizable functions and add-ons created by users. Sleipnir 2 is one of the few browsers to still support Windows 98.

Sleipnir 3 for Windows: Includes tab options, tab groups, Touchpaging to flick between tabs using your mouse, and mouse gestures.

Sleipnir 3 for Mac: Switch tabs by swiping tabs left or right-click; Operate tabs using gestures; TiledTab - Pinch-in on the TrackPad to view a list of tabs; Hold And Go - Hold down on a link to open in the background; Ad Block; Tab groups for managing tabs; Sync bookmarks with other devices using Fenrir Pass; The standard full-screen with Mac OS X Lion[17]

Sleipnir 4 for Windows: Sleipnir 4 for Windows has introduced minor interface improvements; Smart Tabs - adding, positioning and deletion of tabs is determined based on relationship with previous and next tabs; 150 mouse gesture functions added; Google Chrome extensions support.[18]

Sleipnir 4 for Mac: Thumbnail Tab Navigation - open tabs are not shrunk anymore, instead they are presented in a scrollable list, with tab titles appearing on mouse hover; Portal field - a bar with a double functionality of navigation bar and search; TiledTab - view mode that gives an overview of the opened tabs and allows sorting tabs into six groups; Improved gesture controls.[19]

Sleipnir 5 for Windows: Sleipnir 5 for Windows has integrated all of the features introduced in Sleipnir 4 for Mac; Smooth OSX-like font rendering engine introduced; "Site Updates" feature shows personalized recommendations of articles from the often visited sites; Added touch screen support.[20]

Sleipnir 6 for Windows: Sleipnir 6 for Windows adds FavTab for quick navigation to favorite sites;[21] SmartSearch for searching via highlighting;[22] resizable portal field.[23]

Sleipnir 6.5 for Windows: Sleipnir 6.5 for Windows is a customizable web browser that offers advanced tab management, non-member social feeds, mouse gestures and privacy protection features.

Sleipnir Mobile: The following mobile versions of Sleipnir for smartphones have been released: Android, iOS, and Windows Phone.


Early Gecko-based versions of Sleipnir for Windows scored positive reviews from CNET for the design and functionality, most noticeably, for the inclusion of gestures. “The action is very smooth and natural and a lot like scrolling through pages on your phone with your thumb.”[24] The OSX version review by MakeUseOf followed generally the same line while additionally bringing attention to the convenient tab management.[25]

MacWorld, while reviewing Sleipnir 4 for Mac has praised how the URL bar was changed. “Opera pioneered that idea, but Sleipnir’s tabs remain constantly visible and strike a nice balance between being large enough to identify but small enough not to intrude on the main browser window.” Despite this, version 4 was criticized for its poor performance, compared to other browsers using WebKit.[26]

Later versions of Sleipnir received positive reviews from Softpedia, due to the browser's customizability, features and the availability of mobile versions. “Sleipnir proves to be a stable and fast web browser that comes with innovative functions and various customization possibilities. The extra security features, together with smartphone and web apps linking are features that make it a viable alternative to its more popular competitors.”[27]

In 2012, multiple performance tests were performed by Tom's Hardware, where the Android version of Sleipnir was placed on the third spot as the best browser for Android, outrun by Dolphin and Maxthon.[28]

See also


  1. ^ "リリースノート" [Release Notes]. (in Japanese). Retrieved 7 August 2023.
  2. ^ "Sleipnir 4 for Windows - リリースノート" [Sleipnir 4 for Windows - Release Notes]. (in Japanese). Retrieved 7 August 2023.
  3. ^ "「Sleipnir」をMac App Storeで" ["Sleipnir" on the Mac App Store]. Mac App Store (in Japanese). Retrieved 24 June 2021.
  4. ^ "「Sleipnir Mobile」をApp Storeで" ["Sleipnir Mobile" on the App Store]. App Store (in Japanese). Retrieved 9 August 2023.
  5. ^ "Sleipnir Mobile - Web Browser". Google Play. Retrieved 1 February 2023.
  6. ^ "Sleipnir 3 Web Browser for Windows / Mac - Web browsing that links easily with smartphones". Archived from the original on 2016-05-26. Retrieved 2012-05-25.
  7. ^ Corporate Symbol of Fenrir Archived 2012-07-12 at
  8. ^ Translators wanted Sleipnir web browser Windows, Mac, Mobile Archived 2016-06-24 at the Wayback Machine (Fenrir Developer's Blog)
  9. ^ "About language support for each product". Archived from the original on 2016-03-20. Retrieved 2012-05-25.
  10. ^ (in Japanese) 「Sleipnir」「PictBear」の作者のパソコンが盗難に遭い開発中止に!?
  11. ^ (in Japanese) フェンリル、タブブラウザ「Sleipnir」「Grani」のデフォルト検索エンジンをグーグルに:マーケティング - CNET Japan
  12. ^ "Microsoft offers browser choices to Europeans". BBC News. 1 March 2010.
  13. ^ "EU drops Microsoft browser charges with agreement on 'ballot screen'". The Guardian. 16 December 2009.
  14. ^ "Released Sleipnir 5 for Windows with the latest Blink engine". Sleipnir Blog. December 24, 2013. Archived from the original on March 5, 2014. Retrieved May 28, 2014.
  15. ^ WebKit browsers for Windows - Sleipnir 3 joins the list with α3 Archived 2012-05-20 at the Wayback Machine (Fenrir Developer's Blog)
  16. ^ "Chrome, Firefox, Safari, Opera, Edge? Impressive Web Browser Alternatives". Smashing Magazine. 2015-09-23. Retrieved 2015-09-24.
  17. ^ Mac App Store - Sleipnir Browser
  18. ^ "Sleipnir 4 for Windows". Retrieved 20 October 2015.
  19. ^ Rodriguez, Jorge (January 28, 2013). "Sleipnir 4: A Deconstructed Web Browser". Appstorm. Archived from the original on 21 September 2015. Retrieved 9 October 2015.
  20. ^ "The luxury, advanced Web browser drawing text beautifully like professional tools on PC too – Sleipnir 5, released today!". Sleipnir Blog. November 21, 2013. Retrieved 20 October 2015.
  21. ^ "New feature "FavTab" allows quick navigation, even if 100 tabs are open! Released Sleipnir 6 for Windows". Sleipnir Blog. May 29, 2015. Retrieved 20 October 2015.
  22. ^ "Released Sleipnir 6 for Windows (6.1)!". Sleipnir Blog. September 18, 2015. Retrieved 20 October 2015.
  23. ^ "Released Sleipnir 6 for Windows (6.1.5), Sleipnir 4 for Windows (4.4.1)!". Sleipnir Blog. February 19, 2015. Retrieved 20 October 2015.
  24. ^ "Review: Sleipnir 4 has a different take on Web browsers". CNET. March 22, 2012. Retrieved 9 November 2015.
  25. ^ "Sleipnir – A Speedy And Stylish Web Browser [Mac]". MakeUseOf. April 30, 2012. Archived from the original on 4 March 2016. Retrieved 9 November 2015.
  26. ^ "Sleipnir Review". Macworld. April 9, 2013. Retrieved 9 November 2015.
  27. ^ "Sleipnir Review". Softpedia. February 9, 2014. Retrieved 9 November 2015.
  28. ^ "Which Web Browser Should You Run On Your Android Device?". Tom’s Hardware. November 29, 2012. Retrieved 9 November 2015.